diff --git a/.travis.yml b/.travis.yml
index fc1508961db72f..6dc8e2bdbaa6cf 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,3 +2,4 @@ language: node_js
 node_js:
   - node
   - lts/*
+  - 6
diff --git a/CHANGELOG.md b/CHANGELOG.md
index e6fa641e560801..1596d71684aa2f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,73 @@
 # Change Log
 
+## [v10.2.0](https://github.com/w3c/webidl2.js/tree/v10.2.0) (2018-01-30)
+[Full Changelog](https://github.com/w3c/webidl2.js/compare/v10.1.0...v10.2.0)
+
+**Merged pull requests:**
+
+- Type on union idlType [\#135](https://github.com/w3c/webidl2.js/pull/135) ([saschanaz](https://github.com/saschanaz))
+- feat: add argument/return type [\#134](https://github.com/w3c/webidl2.js/pull/134) ([saschanaz](https://github.com/saschanaz))
+- feat: add dictionary/typedef-type [\#133](https://github.com/w3c/webidl2.js/pull/133) ([saschanaz](https://github.com/saschanaz))
+- feat: add const-type for idlTypes  [\#132](https://github.com/w3c/webidl2.js/pull/132) ([saschanaz](https://github.com/saschanaz))
+- feat: add types on idlTypes [\#131](https://github.com/w3c/webidl2.js/pull/131) ([saschanaz](https://github.com/saschanaz))
+- Auto acquisition for parser result changes [\#130](https://github.com/w3c/webidl2.js/pull/130) ([saschanaz](https://github.com/saschanaz))
+
+## [v10.1.0](https://github.com/w3c/webidl2.js/tree/v10.1.0) (2018-01-19)
+[Full Changelog](https://github.com/w3c/webidl2.js/compare/v10.0.0...v10.1.0)
+
+**Closed issues:**
+
+- Support `raises` and `setraises` [\#128](https://github.com/w3c/webidl2.js/issues/128)
+- Support `legacycaller` [\#127](https://github.com/w3c/webidl2.js/issues/127)
+- Improve "No semicolon after enum" message [\#119](https://github.com/w3c/webidl2.js/issues/119)
+
+**Merged pull requests:**
+
+- Let error messages include the current definition name [\#129](https://github.com/w3c/webidl2.js/pull/129) ([saschanaz](https://github.com/saschanaz))
+
+## [v10.0.0](https://github.com/w3c/webidl2.js/tree/v10.0.0) (2017-12-20)
+[Full Changelog](https://github.com/w3c/webidl2.js/compare/v9.0.0...v10.0.0)
+
+**Closed issues:**
+
+-  Always return an array for idlType, etc. [\#113](https://github.com/w3c/webidl2.js/issues/113)
+- Maintain writer.js or not? [\#109](https://github.com/w3c/webidl2.js/issues/109)
+
+**Merged pull requests:**
+
+- Remove typeExtAttrs from docs [\#124](https://github.com/w3c/webidl2.js/pull/124) ([saschanaz](https://github.com/saschanaz))
+- Remove iterator documentation [\#123](https://github.com/w3c/webidl2.js/pull/123) ([saschanaz](https://github.com/saschanaz))
+- Maintain writer.js [\#122](https://github.com/w3c/webidl2.js/pull/122) ([saschanaz](https://github.com/saschanaz))
+- BREAKING CHANGE: remove deprecated iterator operation [\#121](https://github.com/w3c/webidl2.js/pull/121) ([saschanaz](https://github.com/saschanaz))
+- Use for-of on tests [\#120](https://github.com/w3c/webidl2.js/pull/120) ([saschanaz](https://github.com/saschanaz))
+- docs\(README\): iterables ildType is always array [\#118](https://github.com/w3c/webidl2.js/pull/118) ([marcoscaceres](https://github.com/marcoscaceres))
+
+## [v9.0.0](https://github.com/w3c/webidl2.js/tree/v9.0.0) (2017-11-30)
+[Full Changelog](https://github.com/w3c/webidl2.js/compare/v8.1.0...v9.0.0)
+
+**Closed issues:**
+
+- Code quality [\#116](https://github.com/w3c/webidl2.js/issues/116)
+- Unable to parse HTMLAllCollection interface [\#114](https://github.com/w3c/webidl2.js/issues/114)
+- Add support for mixin syntax [\#112](https://github.com/w3c/webidl2.js/issues/112)
+- Whitespace issues [\#111](https://github.com/w3c/webidl2.js/issues/111)
+
+**Merged pull requests:**
+
+- Consistent array type for iterable.idlType [\#117](https://github.com/w3c/webidl2.js/pull/117) ([saschanaz](https://github.com/saschanaz))
+-  Revert "chore: drop Node 6 support \(\#102\)" [\#115](https://github.com/w3c/webidl2.js/pull/115) ([TimothyGu](https://github.com/TimothyGu))
+
+## [v8.1.0](https://github.com/w3c/webidl2.js/tree/v8.1.0) (2017-11-03)
+[Full Changelog](https://github.com/w3c/webidl2.js/compare/v8.0.1...v8.1.0)
+
+**Closed issues:**
+
+- Extended Attributes `rhs` should always be there [\#96](https://github.com/w3c/webidl2.js/issues/96)
+
+**Merged pull requests:**
+
+- Always add rhs property [\#110](https://github.com/w3c/webidl2.js/pull/110) ([saschanaz](https://github.com/saschanaz))
+
 ## [v8.0.1](https://github.com/w3c/webidl2.js/tree/v8.0.1) (2017-11-03)
 [Full Changelog](https://github.com/w3c/webidl2.js/compare/v8.0.0...v8.0.1)
 
@@ -9,7 +77,7 @@
 
 **Merged pull requests:**
 
-- Remove m postfix from all\_ws\(\) [\#108](https://github.com/w3c/webidl2.js/pull/108) ([SaschaNaz](https://github.com/SaschaNaz))
+- Remove m postfix from all\_ws\(\) [\#108](https://github.com/w3c/webidl2.js/pull/108) ([saschanaz](https://github.com/saschanaz))
 
 ## [v8.0.0](https://github.com/w3c/webidl2.js/tree/v8.0.0) (2017-11-03)
 [Full Changelog](https://github.com/w3c/webidl2.js/compare/v7.0.0...v8.0.0)
@@ -21,9 +89,9 @@
 
 **Merged pull requests:**
 
-- Support mixins + includes statements [\#105](https://github.com/w3c/webidl2.js/pull/105) ([SaschaNaz](https://github.com/SaschaNaz))
+- Support mixins + includes statements [\#105](https://github.com/w3c/webidl2.js/pull/105) ([saschanaz](https://github.com/saschanaz))
 - chore: drop Node 6 support [\#102](https://github.com/w3c/webidl2.js/pull/102) ([marcoscaceres](https://github.com/marcoscaceres))
-- BREAKING CHANGE: drop creator support [\#101](https://github.com/w3c/webidl2.js/pull/101) ([SaschaNaz](https://github.com/SaschaNaz))
+- BREAKING CHANGE: drop creator support [\#101](https://github.com/w3c/webidl2.js/pull/101) ([saschanaz](https://github.com/saschanaz))
 - Normalize some whitespace to pass wpt's lint [\#99](https://github.com/w3c/webidl2.js/pull/99) ([foolip](https://github.com/foolip))
 
 ## [v7.0.0](https://github.com/w3c/webidl2.js/tree/v7.0.0) (2017-10-27)
@@ -54,7 +122,7 @@
 
 **Merged pull requests:**
 
-- Use ES2015 syntax for tests [\#88](https://github.com/w3c/webidl2.js/pull/88) ([SaschaNaz](https://github.com/SaschaNaz))
+- Use ES2015 syntax for tests [\#88](https://github.com/w3c/webidl2.js/pull/88) ([saschanaz](https://github.com/saschanaz))
 
 ## [v6.0.0](https://github.com/w3c/webidl2.js/tree/v6.0.0) (2017-10-17)
 [Full Changelog](https://github.com/w3c/webidl2.js/compare/v5.0.0...v6.0.0)
@@ -73,7 +141,7 @@
 
 **Merged pull requests:**
 
-- BREAKING CHANGE: Use ES2015 syntax [\#84](https://github.com/w3c/webidl2.js/pull/84) ([SaschaNaz](https://github.com/SaschaNaz))
+- BREAKING CHANGE: Use ES2015 syntax [\#84](https://github.com/w3c/webidl2.js/pull/84) ([saschanaz](https://github.com/saschanaz))
 
 ## [v4.2.0](https://github.com/w3c/webidl2.js/tree/v4.2.0) (2017-10-16)
 [Full Changelog](https://github.com/w3c/webidl2.js/compare/v4.1.0...v4.2.0)
@@ -85,8 +153,8 @@
 
 **Merged pull requests:**
 
-- Check duplicated names [\#80](https://github.com/w3c/webidl2.js/pull/80) ([SaschaNaz](https://github.com/SaschaNaz))
-- Remove legacycaller [\#79](https://github.com/w3c/webidl2.js/pull/79) ([SaschaNaz](https://github.com/SaschaNaz))
+- Check duplicated names [\#80](https://github.com/w3c/webidl2.js/pull/80) ([saschanaz](https://github.com/saschanaz))
+- Remove legacycaller [\#79](https://github.com/w3c/webidl2.js/pull/79) ([saschanaz](https://github.com/saschanaz))
 - Add "sequence" property to IDL Type AST definition [\#76](https://github.com/w3c/webidl2.js/pull/76) ([lerouche](https://github.com/lerouche))
 
 ## [v4.1.0](https://github.com/w3c/webidl2.js/tree/v4.1.0) (2017-07-04)
@@ -98,7 +166,7 @@
 
 **Merged pull requests:**
 
-- Support TypeWithExtendedAttributes on generics [\#75](https://github.com/w3c/webidl2.js/pull/75) ([SaschaNaz](https://github.com/SaschaNaz))
+- Support TypeWithExtendedAttributes on generics [\#75](https://github.com/w3c/webidl2.js/pull/75) ([saschanaz](https://github.com/saschanaz))
 
 ## [v4.0.0](https://github.com/w3c/webidl2.js/tree/v4.0.0) (2017-06-27)
 [Full Changelog](https://github.com/w3c/webidl2.js/compare/v3.0.2...v4.0.0)
@@ -112,7 +180,7 @@
 **Merged pull requests:**
 
 - BREAKING CHANGE: remove serializers \(closes \#73\) [\#74](https://github.com/w3c/webidl2.js/pull/74) ([marcoscaceres](https://github.com/marcoscaceres))
-- Add documentation for namespaces [\#70](https://github.com/w3c/webidl2.js/pull/70) ([SaschaNaz](https://github.com/SaschaNaz))
+- Add documentation for namespaces [\#70](https://github.com/w3c/webidl2.js/pull/70) ([saschanaz](https://github.com/saschanaz))
 
 ## [v3.0.2](https://github.com/w3c/webidl2.js/tree/v3.0.2) (2017-05-29)
 [Full Changelog](https://github.com/w3c/webidl2.js/compare/v3.0.1...v3.0.2)
@@ -123,7 +191,7 @@
 
 **Merged pull requests:**
 
-- Test for latest LTS/stable node versions [\#69](https://github.com/w3c/webidl2.js/pull/69) ([SaschaNaz](https://github.com/SaschaNaz))
+- Test for latest LTS/stable node versions [\#69](https://github.com/w3c/webidl2.js/pull/69) ([saschanaz](https://github.com/saschanaz))
 
 ## [v3.0.1](https://github.com/w3c/webidl2.js/tree/v3.0.1) (2017-05-18)
 [Full Changelog](https://github.com/w3c/webidl2.js/compare/v2.4.0...v3.0.1)
@@ -135,8 +203,8 @@
 
 **Merged pull requests:**
 
-- Fix whitespace error on parsing extended attributes [\#68](https://github.com/w3c/webidl2.js/pull/68) ([SaschaNaz](https://github.com/SaschaNaz))
-- Remove deprecated IDL arrays and exceptions [\#67](https://github.com/w3c/webidl2.js/pull/67) ([SaschaNaz](https://github.com/SaschaNaz))
+- Fix whitespace error on parsing extended attributes [\#68](https://github.com/w3c/webidl2.js/pull/68) ([saschanaz](https://github.com/saschanaz))
+- Remove deprecated IDL arrays and exceptions [\#67](https://github.com/w3c/webidl2.js/pull/67) ([saschanaz](https://github.com/saschanaz))
 
 ## [v2.4.0](https://github.com/w3c/webidl2.js/tree/v2.4.0) (2017-04-12)
 [Full Changelog](https://github.com/w3c/webidl2.js/compare/v2.1.0...v2.4.0)
@@ -157,7 +225,7 @@
 - Update webidl2.js [\#63](https://github.com/w3c/webidl2.js/pull/63) ([tqeto](https://github.com/tqeto))
 - Remove support for MapClass \(no longer valid in WebIDL\) [\#62](https://github.com/w3c/webidl2.js/pull/62) ([dontcallmedom](https://github.com/dontcallmedom))
 - Add support for annotated types [\#61](https://github.com/w3c/webidl2.js/pull/61) ([dontcallmedom](https://github.com/dontcallmedom))
-- Support namespaces [\#58](https://github.com/w3c/webidl2.js/pull/58) ([SaschaNaz](https://github.com/SaschaNaz))
+- Support namespaces [\#58](https://github.com/w3c/webidl2.js/pull/58) ([saschanaz](https://github.com/saschanaz))
 - Add support for records [\#57](https://github.com/w3c/webidl2.js/pull/57) ([TimothyGu](https://github.com/TimothyGu))
 - Refactor [\#50](https://github.com/w3c/webidl2.js/pull/50) ([marcoscaceres](https://github.com/marcoscaceres))
 - feat\(lib\): add AMD export support \(closes \#48\) [\#49](https://github.com/w3c/webidl2.js/pull/49) ([marcoscaceres](https://github.com/marcoscaceres))
diff --git a/README.md b/README.md
index 93cc78b9c48bd5..8791360d1c132d 100644
--- a/README.md
+++ b/README.md
@@ -310,7 +310,6 @@ A typedef looks like this:
 ```JS
 {
   "type": "typedef",
-  "typeExtAttrs": [],
   "idlType": {
     "sequence": true,
     "generic": "sequence",
@@ -336,8 +335,6 @@ The fields are as follows:
 * `name`: The typedef's name.
 * `idlType`: An [IDL Type](#idl-type) describing what typedef's type.
 * `extAttrs`: A list of [extended attributes](#extended-attributes).
-* `typeExtAttrs`: A list of [extended attributes](#extended-attributes) that apply to the
-type rather than to the typedef as a whole.
 
 ### Implements
 
@@ -489,34 +486,6 @@ The fields are as follows:
 * `value`: The constant value as described by [Const Values](#default-and-const-values)
 * `extAttrs`: A list of [extended attributes](#extended-attributes).
 
-### Iterator Member
-
-Iterator members look like this
-
-```JS
-{
-  "type": "iterator",
-  "getter": false,
-  "setter": false,
-  "deleter": false,
-  "static": false,
-  "stringifier": false,
-  "idlType": {
-    "sequence": false,
-    "generic": null,
-    "nullable": false,
-    "union": false,
-    "idlType": "Session2"
-  },
-  "iteratorObject": "SessionIterator",
-  "extAttrs": []
-}
-```
-
-* `type`: Always "iterator".
-* `iteratorObject`: The string on the right-hand side; absent if there isn't one.
-* the rest: same as on [operations](#operation-member).
-
 ### Arguments
 
 The arguments (e.g. for an operation) look like this:
@@ -611,7 +580,7 @@ These appear as members of interfaces that look like this:
 The fields are as follows:
 
 * `type`: Always one of "iterable", "legacyiterable", "maplike" or "setlike".
-* `idlType`: An [IDL Type](#idl-type) (or an array of two types) representing the declared type arguments.
+* `idlType`: An array with one or more [IDL Types](#idl-type) representing the declared type arguments.
 * `readonly`: Whether the maplike or setlike is declared as read only.
 * `extAttrs`: A list of [extended attributes](#extended-attributes).
 
diff --git a/lib/webidl2.js b/lib/webidl2.js
index 2f116c40d94bfc..a7a61d957b55c5 100644
--- a/lib/webidl2.js
+++ b/lib/webidl2.js
@@ -1,32 +1,82 @@
 "use strict";
 
 (() => {
+  // These regular expressions use the sticky flag so they will only match at
+  // the current location (ie. the offset of lastIndex).
+  const tokenRe = {
+    // This expression uses a lookahead assertion to catch false matches
+    // against integers early.
+    "float": /-?(?=[0-9]*\.|[0-9]+[eE])(([0-9]+\.[0-9]*|[0-9]*\.[0-9]+)([Ee][-+]?[0-9]+)?|[0-9]+[Ee][-+]?[0-9]+)/y,
+    "integer": /-?(0([Xx][0-9A-Fa-f]+|[0-7]*)|[1-9][0-9]*)/y,
+    "identifier": /[A-Z_a-z][0-9A-Z_a-z-]*/y,
+    "string": /"[^"]*"/y,
+    "whitespace": /[\t\n\r ]+/y,
+    "comment": /((\/(\/.*|\*([^*]|\*[^\/])*\*\/)[\t\n\r ]*)+)/y,
+    "other": /[^\t\n\r 0-9A-Z_a-z]/y
+  };
+
+  function attemptTokenMatch(str, type, re, lastIndex, tokens) {
+    re.lastIndex = lastIndex;
+    const result = re.exec(str);
+    if (result) {
+      tokens.push({ type, value: result[0] });
+      return re.lastIndex;
+    }
+    return -1;
+  }
+
   function tokenise(str) {
     const tokens = [];
-    const re = {
-      "float": /^-?(([0-9]+\.[0-9]*|[0-9]*\.[0-9]+)([Ee][-+]?[0-9]+)?|[0-9]+[Ee][-+]?[0-9]+)/,
-      "integer": /^-?(0([Xx][0-9A-Fa-f]+|[0-7]*)|[1-9][0-9]*)/,
-      "identifier": /^[A-Z_a-z][0-9A-Z_a-z-]*/,
-      "string": /^"[^"]*"/,
-      "whitespace": /^(?:[\t\n\r ]+|[\t\n\r ]*((\/\/.*|\/\*(.|\n|\r)*?\*\/)[\t\n\r ]*))+/,
-      "other": /^[^\t\n\r 0-9A-Z_a-z]/
-    };
-    const types = ["float", "integer", "identifier", "string", "whitespace", "other"];
-    while (str.length > 0) {
-      let matched = false;
-      for (const type of types) {
-        str = str.replace(re[type], tok => {
-          tokens.push({ type, value: tok });
-          matched = true;
-          return "";
-        });
-        if (matched) break;
+    let lastIndex = 0;
+    while (lastIndex < str.length) {
+      const nextChar = str.charAt(lastIndex);
+      let result = -1;
+      if (/[-0-9.]/.test(nextChar)) {
+        result = attemptTokenMatch(str, "float", tokenRe.float, lastIndex,
+                                   tokens);
+        if (result === -1) {
+          result = attemptTokenMatch(str, "integer", tokenRe.integer, lastIndex,
+                                     tokens);
+        }
+        if (result === -1) {
+          // '-' and '.' can also match "other".
+          result = attemptTokenMatch(str, "other", tokenRe.other,
+                                     lastIndex, tokens);
+        }
+      } else if (/[A-Z_a-z]/.test(nextChar)) {
+        result = attemptTokenMatch(str, "identifier", tokenRe.identifier,
+                                   lastIndex, tokens);
+      } else if (nextChar === '"') {
+        result = attemptTokenMatch(str, "string", tokenRe.string,
+                                   lastIndex, tokens);
+        if (result === -1) {
+          // '"' can also match "other".
+          result = attemptTokenMatch(str, "other", tokenRe.other,
+                                     lastIndex, tokens);
+        }
+      } else if (/[\t\n\r ]/.test(nextChar)) {
+        result = attemptTokenMatch(str, "whitespace", tokenRe.whitespace,
+                                   lastIndex, tokens);
+      } else if (nextChar === '/') {
+        // The parser expects comments to be labelled as "whitespace".
+        result = attemptTokenMatch(str, "whitespace", tokenRe.comment,
+                                   lastIndex, tokens);
+        if (result === -1) {
+          // '/' can also match "other".
+          result = attemptTokenMatch(str, "other", tokenRe.other,
+                                     lastIndex, tokens);
+        }
+      } else {
+        result = attemptTokenMatch(str, "other", tokenRe.other,
+                                   lastIndex, tokens);
+      }
+      if (result === -1) {
+        throw new Error("Token stream not progressing");
       }
-      if (matched) continue;
-      throw new Error("Token stream not progressing");
+      lastIndex = result;
     }
     return tokens;
-  };
+  }
 
   class WebIDLParseError {
     constructor(str, line, input, tokens) {
@@ -45,6 +95,7 @@
     let line = 1;
     tokens = tokens.slice();
     const names = new Map();
+    let current = null;
 
     const FLOAT = "float";
     const INT = "integer";
@@ -57,7 +108,7 @@
       getter: false,
       setter: false,
       deleter: false,
-      "static": false,
+      static: false,
       stringifier: false
     });
 
@@ -69,8 +120,18 @@
         tok += tokens[numTokens].value;
         numTokens++;
       }
-      throw new WebIDLParseError(str, line, tok, tokens.slice(0, maxTokens));
-    };
+      
+      let message;
+      if (current) {
+        message = `Got an error during or right after parsing \`${current.partial ? "partial " : ""}${current.type} ${current.name}\`: ${str}`
+      }
+      else {
+        // throwing before any valid definition
+        message = `Got an error before parsing any named definition: ${str}`;
+      }
+
+      throw new WebIDLParseError(message, line, tok, tokens.slice(0, maxTokens));
+    }
 
     function sanitize_name(name, type) {
       if (names.has(name)) {
@@ -86,23 +147,34 @@
       if (!tokens.length || tokens[0].type !== type) return;
       if (typeof value === "undefined" || tokens[0].value === value) {
         last_token = tokens.shift();
-        if (type === ID) last_token.value = last_token.value.replace(/^_/, "");
+        if (type === ID && last_token.value.startsWith('_'))
+          last_token.value = last_token.value.substring(1);
         return last_token;
       }
-    };
+    }
+
+    function count(str, char) {
+      let total = 0;
+      for (let i = str.indexOf(char); i !== -1; i = str.indexOf(char, i + 1)) {
+        ++total;
+      }
+      return total;
+    }
 
     function ws() {
       if (!tokens.length) return;
       if (tokens[0].type === "whitespace") {
         const t = tokens.shift();
-        t.value.replace(/\n/g, m => {
-          line++;
-          return m;
-        });
+        line += count(t.value, '\n');
         return t;
       }
-    };
+    }
 
+    const all_ws_re = {
+      "ws": /([\t\n\r ]+)/y,
+      "line-comment": /\/\/(.*)\r?\n?/y,
+      "multiline-comment": /\/\*((?:[^*]|\*[^/])*)\*\//y
+    };
     function all_ws(store, pea) { // pea == post extended attribute, tpea = same for types
       const t = { type: "whitespace", value: "" };
       while (true) {
@@ -113,30 +185,30 @@
       if (t.value.length > 0) {
         if (store) {
           let w = t.value;
-          const re = {
-            "ws": /^([\t\n\r ]+)/,
-            "line-comment": /^\/\/(.*)\r?\n?/,
-            "multiline-comment": /^\/\*((?:.|\n|\r)*?)\*\//
-          };
-          const wsTypes = [];
-          for (const k in re) wsTypes.push(k);
-          while (w.length) {
+          let lastIndex = 0;
+          while (lastIndex < w.length) {
             let matched = false;
-            for (const type of wsTypes) {
-              w = w.replace(re[type], (tok, m1) => {
-                store.push({ type: type + (pea ? ("-" + pea) : ""), value: m1 });
+            // Servo doesn't support using "const" in this construction yet.
+            // See https://github.com/servo/servo/issues/20231.
+            // |type| can be made const once Servo supports it.
+            for (let type in all_ws_re) {
+              const re = all_ws_re[type];
+              re.lastIndex = lastIndex;
+              const result = re.exec(w);
+              if (result) {
+                store.push({ type: type + (pea ? ("-" + pea) : ""), value: result[1] });
                 matched = true;
-                return "";
-              });
-              if (matched) break;
+                lastIndex = re.lastIndex;
+                break;
+              }
             }
-            if (matched) continue;
-            throw new Error("Surprising white space construct."); // this shouldn't happen
+            if (!matched)
+              throw new Error("Surprising white space construct."); // this shouldn't happen
           }
         }
         return t;
       }
-    };
+    }
 
     function integer_type() {
       let ret = "";
@@ -151,7 +223,7 @@
         return ret;
       }
       if (ret) error("Failed to parse integer type");
-    };
+    }
 
     function float_type() {
       let ret = "";
@@ -161,7 +233,7 @@
       if (consume(ID, "float")) return ret + "float";
       if (consume(ID, "double")) return ret + "double";
       if (ret) error("Failed to parse float type");
-    };
+    }
 
     function primitive_type() {
       const num_type = integer_type() || float_type();
@@ -170,7 +242,7 @@
       if (consume(ID, "boolean")) return "boolean";
       if (consume(ID, "byte")) return "byte";
       if (consume(ID, "octet")) return "octet";
-    };
+    }
 
     function const_value() {
       if (consume(ID, "true")) return { type: "boolean", value: true };
@@ -185,7 +257,7 @@
         if (consume(ID, "Infinity")) return { type: "Infinity", negative: true };
         else tokens.unshift(tok);
       }
-    };
+    }
 
     function type_suffix(obj) {
       while (true) {
@@ -195,11 +267,11 @@
           obj.nullable = true;
         } else return;
       }
-    };
+    }
 
-    function single_type() {
+    function single_type(typeName) {
       const prim = primitive_type();
-      const ret = { sequence: false, generic: null, nullable: false, union: false };
+      const ret = { type: typeName || null, sequence: false, generic: null, nullable: false, union: false };
       let name;
       let value;
       if (prim) {
@@ -217,7 +289,7 @@
           const types = [];
           do {
             all_ws();
-            types.push(type_with_extended_attributes() || error("Error parsing generic type " + value));
+            types.push(type_with_extended_attributes(typeName) || error("Error parsing generic type " + value));
             all_ws();
           }
           while (consume(OTHER, ","));
@@ -246,12 +318,12 @@
       type_suffix(ret);
       if (ret.nullable && ret.idlType === "any") error("Type any cannot be made nullable");
       return ret;
-    };
+    }
 
-    function union_type() {
+    function union_type(typeName) {
       all_ws();
       if (!consume(OTHER, "(")) return;
-      const ret = { sequence: false, generic: null, nullable: false, union: true, idlType: [] };
+      const ret = { type: typeName || null, sequence: false, generic: null, nullable: false, union: true, idlType: [] };
       const fst = type_with_extended_attributes() || error("Union type with no content");
       ret.idlType.push(fst);
       while (true) {
@@ -263,18 +335,18 @@
       if (!consume(OTHER, ")")) error("Unterminated union type");
       type_suffix(ret);
       return ret;
-    };
+    }
 
-    function type() {
-      return single_type() || union_type();
-    };
+    function type(typeName) {
+      return single_type(typeName) || union_type(typeName);
+    }
 
-    function type_with_extended_attributes() {
+    function type_with_extended_attributes(typeName) {
       const extAttrs = extended_attrs();
-      const ret = single_type() || union_type();
+      const ret = single_type(typeName) || union_type(typeName);
       if (extAttrs.length && ret) ret.extAttrs = extAttrs;
       return ret;
-    };
+    }
 
     function argument(store) {
       const ret = { optional: false, variadic: false };
@@ -285,7 +357,7 @@
         ret.optional = true;
         all_ws();
       }
-      ret.idlType = type_with_extended_attributes();
+      ret.idlType = type_with_extended_attributes("argument-type");
       if (!ret.idlType) {
         if (opt_token) tokens.unshift(opt_token);
         return;
@@ -320,7 +392,7 @@
         }
       }
       return ret;
-    };
+    }
 
     function argument_list(store) {
       const ret = [];
@@ -333,7 +405,7 @@
         const nxt = argument(store ? ret : null) || error("Trailing comma in arguments list");
         ret.push(nxt);
       }
-    };
+    }
 
     function simple_extended_attr(store) {
       all_ws();
@@ -384,7 +456,7 @@
         consume(OTHER, ")") || error("Unexpected token in extended attribute argument list");
       }
       return ret;
-    };
+    }
 
     // Note: we parse something simpler than the official syntax. It's all that ever
     // seems to be used
@@ -404,7 +476,7 @@
       all_ws();
       consume(OTHER, "]") || error("No end of extended attribute");
       return eas;
-    };
+    }
 
     function default_() {
       all_ws();
@@ -418,11 +490,11 @@
           return { type: "sequence", value: [] };
         } else {
           const str = consume(STR) || error("No value for default");
-          str.value = str.value.replace(/^"/, "").replace(/"$/, "");
+          str.value = str.value.slice(1, -1);
           return str;
         }
       }
-    };
+    }
 
     function const_(store) {
       all_ws(store, "pea");
@@ -434,7 +506,7 @@
         typ = consume(ID) || error("No type for const");
         typ = typ.value;
       }
-      ret.idlType = typ;
+      ret.idlType = { type: "const-type", idlType: typ };
       all_ws();
       if (consume(OTHER, "?")) {
         ret.nullable = true;
@@ -451,7 +523,7 @@
       all_ws();
       consume(OTHER, ";") || error("Unterminated const");
       return ret;
-    };
+    }
 
     function inheritance() {
       all_ws();
@@ -460,7 +532,7 @@
         const inh = consume(ID) || error("No type in inheritance");
         return inh.value;
       }
-    };
+    }
 
     function operation_rest(ret, store) {
       all_ws();
@@ -475,7 +547,7 @@
       all_ws();
       consume(OTHER, ";") || error("Unterminated operation");
       return ret;
-    };
+    }
 
     function callback(store) {
       all_ws(store, "pea");
@@ -484,12 +556,11 @@
       all_ws();
       const tok = consume(ID, "interface");
       if (tok) {
-        ret = interface_rest();
-        ret.type = "callback interface";
+        ret = interface_rest(false, store, "callback interface");
         return ret;
       }
       const name = consume(ID) || error("No name for callback");
-      ret = { type: "callback", name: sanitize_name(name.value, "callback") };
+      ret = current = { type: "callback", name: sanitize_name(name.value, "callback") };
       all_ws();
       consume(OTHER, "=") || error("No assignment in callback");
       all_ws();
@@ -502,14 +573,14 @@
       all_ws();
       consume(OTHER, ";") || error("Unterminated callback");
       return ret;
-    };
+    }
 
     function attribute(store) {
       all_ws(store, "pea");
       const grabbed = [];
       const ret = {
         type: "attribute",
-        "static": false,
+        static: false,
         stringifier: false,
         inherit: false,
         readonly: false
@@ -517,7 +588,7 @@
       const w = all_ws();
       if (w) grabbed.push(w);
       if (consume(ID, "inherit")) {
-        if (ret["static"] || ret.stringifier) error("Cannot have a static or stringifier inherit");
+        if (ret.static || ret.stringifier) error("Cannot have a static or stringifier inherit");
         ret.inherit = true;
         grabbed.push(last_token);
         const w = all_ws();
@@ -534,14 +605,14 @@
         tokens = grabbed.concat(tokens);
       }
       return rest;
-    };
+    }
 
     function attribute_rest(ret) {
       if (!consume(ID, "attribute")) {
         return;
       }
       all_ws();
-      ret.idlType = type_with_extended_attributes() || error("No type in attribute");
+      ret.idlType = type_with_extended_attributes("attribute-type") || error("No type in attribute");
       if (ret.idlType.sequence) error("Attributes cannot accept sequence types");
       if (ret.idlType.generic === "record") error("Attributes cannot accept record types");
       all_ws();
@@ -550,17 +621,17 @@
       all_ws();
       consume(OTHER, ";") || error("Unterminated attribute");
       return ret;
-    };
+    }
 
     function return_type() {
-      const typ = type();
+      const typ = type("return-type");
       if (!typ) {
         if (consume(ID, "void")) {
           return "void";
         } else error("No return type");
       }
       return typ;
-    };
+    }
 
     function operation(store) {
       all_ws(store, "pea");
@@ -580,24 +651,9 @@
       }
       ret.idlType = return_type();
       all_ws();
-      if (consume(ID, "iterator")) {
-        all_ws();
-        ret.type = "iterator";
-        if (consume(ID, "object")) {
-          ret.iteratorObject = "object";
-        } else if (consume(OTHER, "=")) {
-          all_ws();
-          var name = consume(ID) || error("No right hand side in iterator");
-          ret.iteratorObject = name.value;
-        }
-        all_ws();
-        consume(OTHER, ";") || error("Unterminated iterator");
-        return ret;
-      } else {
-        operation_rest(ret, store);
-        return ret;
-      }
-    };
+      operation_rest(ret, store);
+      return ret;
+    }
 
     function static_member(store) {
       all_ws(store, "pea");
@@ -629,7 +685,7 @@
           arr.push(name.value);
         } else break;
       }
-    };
+    }
 
     function iterable_type() {
       if (consume(ID, "iterable")) return "iterable";
@@ -637,13 +693,13 @@
       else if (consume(ID, "maplike")) return "maplike";
       else if (consume(ID, "setlike")) return "setlike";
       else return;
-    };
+    }
 
     function readonly_iterable_type() {
       if (consume(ID, "maplike")) return "maplike";
       else if (consume(ID, "setlike")) return "setlike";
       else return;
-    };
+    }
 
     function iterable(store) {
       all_ws(store, "pea");
@@ -670,17 +726,14 @@
         delete ret.readonly;
       all_ws();
       if (consume(OTHER, "<")) {
-        ret.idlType = type_with_extended_attributes() || error(`Error parsing ${ittype} declaration`);
+        ret.idlType = [type_with_extended_attributes()] || error(`Error parsing ${ittype} declaration`);
         all_ws();
         if (secondTypeAllowed) {
-          let type2 = null;
           if (consume(OTHER, ",")) {
             all_ws();
-            type2 = type_with_extended_attributes();
+            ret.idlType.push(type_with_extended_attributes());
             all_ws();
           }
-          if (type2)
-            ret.idlType = [ret.idlType, type2];
           else if (secondTypeRequired)
             error(`Missing second type argument in ${ittype} declaration`);
         }
@@ -691,16 +744,16 @@
         error(`Error parsing ${ittype} declaration`);
 
       return ret;
-    };
+    }
 
-    function interface_rest(isPartial, store) {
+    function interface_rest(isPartial, store, typeName = "interface") {
       all_ws();
       const name = consume(ID) || error("No name for interface");
       const mems = [];
-      const ret = {
-        type: "interface",
+      const ret = current = {
+        type: typeName,
         name: isPartial ? name.value : sanitize_name(name.value, "interface"),
-        partial: false,
+        partial: isPartial,
         members: mems
       };
       if (!isPartial) ret.inheritance = inheritance() || null;
@@ -731,7 +784,7 @@
         mem.extAttrs = ea;
         ret.members.push(mem);
       }
-    };
+    }
 
     function mixin_rest(isPartial, store) {
       all_ws();
@@ -739,10 +792,10 @@
       all_ws();
       const name = consume(ID) || error("No name for interface mixin");
       const mems = [];
-      const ret = {
+      const ret = current = {
         type: "interface mixin",
         name: isPartial ? name.value : sanitize_name(name.value, "interface mixin"),
-        partial: false,
+        partial: isPartial,
         members: mems
       };
       all_ws();
@@ -785,7 +838,7 @@
       all_ws();
       const name = consume(ID) || error("No name for namespace");
       const mems = [];
-      const ret = {
+      const ret = current = {
         type: "namespace",
         name: isPartial ? name.value : sanitize_name(name.value, "namespace"),
         partial: isPartial,
@@ -815,7 +868,7 @@
       const grabbed = [];
       const ret = {
         type: "attribute",
-        "static": false,
+        static: false,
         stringifier: false,
         inherit: false,
         readonly: false
@@ -854,9 +907,8 @@
         interface_(true, store) ||
         namespace(true, store) ||
         error("Partial doesn't apply to anything");
-      thing.partial = true;
       return thing;
-    };
+    }
 
     function dictionary(isPartial, store) {
       all_ws(isPartial ? null : store, "pea");
@@ -864,10 +916,10 @@
       all_ws();
       const name = consume(ID) || error("No name for dictionary");
       const mems = [];
-      const ret = {
+      const ret = current = {
         type: "dictionary",
         name: isPartial ? name.value : sanitize_name(name.value, "dictionary"),
-        partial: false,
+        partial: isPartial,
         members: mems
       };
       if (!isPartial) ret.inheritance = inheritance() || null;
@@ -883,7 +935,7 @@
         const ea = extended_attrs(store ? mems : null);
         all_ws(store ? mems : null, "pea");
         const required = consume(ID, "required");
-        const typ = type_with_extended_attributes() || error("No type for dictionary member");
+        const typ = type_with_extended_attributes("dictionary-type") || error("No type for dictionary member");
         all_ws();
         const name = consume(ID) || error("No name for dictionary member");
         const dflt = default_();
@@ -902,7 +954,7 @@
         all_ws();
         consume(OTHER, ";") || error("Unterminated dictionary member");
       }
-    };
+    }
 
     function enum_(store) {
       all_ws(store, "pea");
@@ -910,7 +962,7 @@
       all_ws();
       const name = consume(ID) || error("No name for enum");
       const vals = [];
-      const ret = {
+      const ret = current = {
         type: "enum",
         name: sanitize_name(name.value, "enum"),
         values: vals
@@ -926,7 +978,7 @@
           return ret;
         }
         const val = consume(STR) || error("Unexpected value in enum");
-        val.value = val.value.replace(/"/g, "");
+        val.value = val.value.slice(1, -1);
         ret.values.push(val);
         all_ws(store ? vals : null);
         if (consume(OTHER, ",")) {
@@ -937,7 +989,7 @@
           saw_comma = false;
         }
       }
-    };
+    }
 
     function typedef(store) {
       all_ws(store, "pea");
@@ -946,14 +998,15 @@
         type: "typedef"
       };
       all_ws();
-      ret.idlType = type_with_extended_attributes() || error("No type in typedef");
+      ret.idlType = type_with_extended_attributes("typedef-type") || error("No type in typedef");
       all_ws();
       const name = consume(ID) || error("No name in typedef");
       ret.name = sanitize_name(name.value, "typedef");
+      current = ret;
       all_ws();
       consume(OTHER, ";") || error("Unterminated typedef");
       return ret;
-    };
+    }
 
     function implements_(store) {
       all_ws(store, "pea");
@@ -976,7 +1029,7 @@
         tokens.unshift(w);
         tokens.unshift(target);
       }
-    };
+    }
 
     function includes(store) {
       all_ws(store, "pea");
@@ -999,7 +1052,7 @@
         tokens.unshift(w);
         tokens.unshift(target);
       }
-    };
+    }
 
     function definition(store) {
       return callback(store) ||
@@ -1011,7 +1064,7 @@
         implements_(store) ||
         includes(store) ||
         namespace(false, store);
-    };
+    }
 
     function definitions(store) {
       if (!tokens.length) return [];
@@ -1027,11 +1080,11 @@
         defs.push(def);
       }
       return defs;
-    };
+    }
     const res = definitions(opt.ws);
     if (tokens.length) error("Unrecognised tokens");
     return res;
-  };
+  }
 
   const obj = {
     parse(str, opt) {
diff --git a/lib/writer.js b/lib/writer.js
index 5e30e707e13c54..c00c0dd932221b 100644
--- a/lib/writer.js
+++ b/lib/writer.js
@@ -1,78 +1,71 @@
-(function() {
+"use strict";
 
-  var write = function(ast, opt) {
-    var curPea = "",
-      curTPea = "",
-      opt = opt || {},
-      noop = function(str) {
-        return str; },
-      optNames = "type".split(" "),
-      context = [];
-    for (var i = 0, n = optNames.length; i < n; i++) {
-      var o = optNames[i];
+(() => {
+  function write(ast, opt = {}) {
+    let curPea = "";
+    let curTPea = "";
+    const noop = str => str;
+    const optNames = "type".split(" ");
+    const context = [];
+    for (const o of optNames) {
       if (!opt[o]) opt[o] = noop;
     }
 
-    var literal = function(it) {
+    function literal(it) {
       return it.value;
     };
-    var wsPea = function(it) {
+    function wsPea(it) {
       curPea += it.value;
       return "";
     };
-    var wsTPea = function(it) {
+    function wsTPea(it) {
       curTPea += it.value;
       return "";
     };
-    var lineComment = function(it) {
-      return "//" + it.value + "\n";
+    function lineComment(it) {
+      return `//${it.value}\n`;
     };
-    var multilineComment = function(it) {
-      return "/*" + it.value + "*/";
+    function multilineComment(it) {
+      return `/*${it.value}*/`;
     };
-    var type = function(it) {
+    function type(it) {
       if (typeof it === "string") return opt.type(it); // XXX should maintain some context
-      if (it.union) return "(" + it.idlType.map(type).join(" or ") + ")";
-      var ret = "";
-      if (it.generic) ret += it.generic + "<";
-      else if (it.sequence) ret += "sequence<";
-      if (Array.isArray(it.idlType)) ret += it.idlType.map(type).join(", ");
-      else ret += type(it.idlType);
-      if (it.array || it.generic === 'Array') {
-        for (var i = 0, n = it.nullableArray.length; i < n; i++) {
-          var val = it.nullableArray[i];
-          if (val) ret += "?";
-          ret += "[]";
-        }
+      let ret = extended_attributes(it.extAttrs, curPea);
+      if (it.union) ret += `(${it.idlType.map(type).join(" or ")})`;
+      else {
+        if (it.generic) ret += `${it.generic}<`;
+        if (Array.isArray(it.idlType)) ret += it.idlType.map(type).join(", ");
+        else ret += type(it.idlType);
+        if (it.generic) ret += ">";
       }
-      if (it.generic || it.sequence) ret += ">";
       if (it.nullable) ret += "?";
 
       return ret;
     };
-    var const_value = function(it) {
-      var tp = it.type;
+    function const_value(it) {
+      const tp = it.type;
       if (tp === "boolean") return it.value ? "true" : "false";
       else if (tp === "null") return "null";
       else if (tp === "Infinity") return (it.negative ? "-" : "") + "Infinity";
       else if (tp === "NaN") return "NaN";
       else if (tp === "number") return it.value;
-      else return '"' + it.value + '"';
+      else if (tp === "sequence") return "[]";
+      else return `"${it.value}"`;
     };
-    var argument = function(arg, pea) {
-      var ret = extended_attributes(arg.extAttrs, pea);
+    function argument(arg, pea) {
+      let ret = extended_attributes(arg.extAttrs, pea);
       if (arg.optional) ret += "optional ";
       ret += type(arg.idlType);
       if (arg.variadic) ret += "...";
-      ret += " " + arg.name;
-      if (arg["default"]) ret += " = " + const_value(arg["default"]);
+      ret += ` ${arg.name}`;
+      if (arg["default"]) ret += ` = ${const_value(arg["default"])}`;
       return ret;
     };
-    var args = function(its) {
-      var res = "",
-        pea = "";
-      for (var i = 0, n = its.length; i < n; i++) {
-        var arg = its[i];
+    function args(its) {
+      let res = "";
+      let pea = "";
+      for (let i = 0, n = its.length; i < n; i++) {
+        const arg = its[i];
         if (arg.type === "ws") res += arg.value;
         else if (arg.type === "ws-pea") pea += arg.value;
         else {
@@ -83,182 +76,198 @@
       }
       return res;
     };
-    var make_ext_at = function(it) {
-      if (it["arguments"] === null) return it.name;
+    function make_ext_at(it) {
       context.unshift(it);
-      var ret = it.name + "(" + (it["arguments"].length ? args(it["arguments"]) : "") + ")";
+      let ret = it.name;
+      if (it.rhs) {
+        if (it.rhs.type === "identifier-list") ret += `=(${it.rhs.value.join(',')})`;
+        else ret += `=${it.rhs.value}`;
+      }
+      if (it.arguments) ret += `(${it["arguments"].length ? args(it["arguments"]) : ""})`;
       context.shift(); // XXX need to add more contexts, but not more than needed for ReSpec
       return ret;
     };
-    var extended_attributes = function(eats, pea) {
+    function extended_attributes(eats, pea) {
       if (!eats || !eats.length) return "";
-      return "[" + eats.map(make_ext_at).join(", ") + "]" + pea;
+      return `[${eats.map(make_ext_at).join(", ")}]${pea}`;
     };
 
-    var modifiers = "getter setter creator deleter legacycaller stringifier static".split(" ");
-    var operation = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    const modifiers = "getter setter creator deleter legacycaller stringifier static".split(" ");
+    function operation(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
       if (it.stringifier && !it.idlType) return "stringifier;";
-      for (var i = 0, n = modifiers.length; i < n; i++) {
-        var mod = modifiers[i];
+      for (const mod of modifiers) {
         if (it[mod]) ret += mod + " ";
       }
       ret += type(it.idlType) + " ";
       if (it.name) ret += it.name;
-      ret += "(" + args(it["arguments"]) + ");";
+      ret += `(${args(it["arguments"])});`;
       return ret;
     };
 
-    var attribute = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function attribute(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
       if (it["static"]) ret += "static ";
       if (it.stringifier) ret += "stringifier ";
       if (it.readonly) ret += "readonly ";
       if (it.inherit) ret += "inherit ";
-      ret += "attribute " + type(it.idlType) + " " + it.name + ";";
+      ret += `attribute ${type(it.idlType)} ${it.name};`;
       return ret;
     };
 
-    var interface_ = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function interface_(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
       if (it.partial) ret += "partial ";
-      ret += "interface " + it.name + " ";
-      if (it.inheritance) ret += ": " + it.inheritance + " ";
-      ret += "{" + iterate(it.members) + "};";
+      ret += `interface ${it.name} `;
+      if (it.inheritance) ret += `: ${it.inheritance} `;
+      ret += `{${iterate(it.members)}};`;
       return ret;
     };
 
-    var dictionary = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function interface_mixin(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
       if (it.partial) ret += "partial ";
-      ret += "dictionary " + it.name + " ";
-      ret += "{" + iterate(it.members) + "};";
+      ret += `interface mixin ${it.name} `;
+      ret += `{${iterate(it.members)}};`;
+      return ret;
+    }
+
+    function namespace(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
+      curPea = "";
+      if (it.partial) ret += "partial ";
+      ret += `namespace ${it.name} `;
+      ret += `{${iterate(it.members)}};`;
+      return ret;
+    }
+
+    function dictionary(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
+      curPea = "";
+      if (it.partial) ret += "partial ";
+      ret += `dictionary ${it.name} `;
+      if (it.inheritance) ret += `: ${it.inheritance} `;
+      ret += `{${iterate(it.members)}};`;
       return ret;
     };
-    var field = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function field(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
       if (it.required) ret += "required ";
-      ret += type(it.idlType) + " " + it.name;
-      if (it["default"]) ret += " = " + const_value(it["default"]);
+      ret += `${type(it.idlType)} ${it.name}`;
+      if (it["default"]) ret += ` = ${const_value(it["default"])}`;
       ret += ";";
       return ret;
     };
-    var exception = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function const_(it) {
+      const ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
-      ret += "exception " + it.name + " ";
-      if (it.inheritance) ret += ": " + it.inheritance + " ";
-      ret += "{" + iterate(it.members) + "};";
-      return ret;
+      return `${ret}const ${type(it.idlType)}${it.nullable ? "?" : ""} ${it.name} = ${const_value(it.value)};`;
     };
-    var const_ = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function typedef(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
-      return ret + "const " + type(it.idlType) + " " + it.name + " = " + const_value(it.value) + ";";
+      ret += `typedef ${extended_attributes(it.typeExtAttrs, curTPea)}`;
+      curTPea = "";
+      return `${ret}${type(it.idlType)} ${it.name};`;
     };
-    var typedef = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function implements_(it) {
+      const ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
-      ret += "typedef " + extended_attributes(it.typeExtAttrs, curTPea);
-      curTPea = "";
-      return ret + type(it.idlType) + " " + it.name + ";";
+      return `${ret}${it.target} implements ${it["implements"]};`;
     };
-    var implements_ = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function includes(it) {
+      const ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
-      return ret + it.target + " implements " + it["implements"] + ";";
+      return `${ret}${it.target} includes ${it.includes};`;
     };
-    var callback = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function callback(it) {
+      const ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
-      return ret + "callback " + it.name + " = " + type(it.idlType) +
-        "(" + args(it["arguments"]) + ");";
+      return `${ret}callback ${it.name} = ${type(it.idlType)}(${args(it["arguments"])});`;
     };
-    var enum_ = function(it) {
-      var ret = extended_attributes(it.extAttrs, curPea);
+    function enum_(it) {
+      let ret = extended_attributes(it.extAttrs, curPea);
       curPea = "";
-      ret += "enum " + it.name + " {";
-      for (var i = 0, n = it.values.length; i < n; i++) {
-        var v = it.values[i];
-        if (typeof v === "string") ret += '"' + v + '"';
+      ret += `enum ${it.name} {`;
+      for (const v of it.values) {
+        if (v.type === "string") ret += `"${v.value}"`;
         else if (v.type === "ws") ret += v.value;
         else if (v.type === ",") ret += ",";
       }
       return ret + "};";
     };
-    var iterable = function(it) {
-      return "iterable<" + (it.idlType instanceof Array ? it.idlType.map(type).join(", ") : type(it.idlType)) + ">;";
+    function iterable(it) {
+      return `iterable<${Array.isArray(it.idlType) ? it.idlType.map(type).join(", ") : type(it.idlType)}>;`;
     };
-    var legacyiterable = function(it) {
-      return "legacyiterable<" + (it.idlType instanceof Array ? it.idlType.map(type).join(", ") : type(it.idlType)) + ">;";
+    function legacyiterable(it) {
+      return `legacyiterable<${Array.isArray(it.idlType) ? it.idlType.map(type).join(", ") : type(it.idlType)}>;`;
     };
-    var maplike = function(it) {
-      return (it.readonly ? "readonly " : "") + "maplike<" +
-        it.idlType.map(type).join(", ") + ">;";
+    function maplike(it) {
+      return `${it.readonly ? "readonly " : ""}maplike<${it.idlType.map(type).join(", ")}>;`;
     };
-    var setlike = function(it) {
-      return (it.readonly ? "readonly " : "") + "setlike<" +
-        type(it.idlType) + ">;";
+    function setlike(it) {
+      return `${it.readonly ? "readonly " : ""}setlike<${type(it.idlType[0])}>;`;
     };
-    var callbackInterface = function(it) {
-      return 'callback ' + interface_(it);
+    function callbackInterface(it) {
+      return `callback ${interface_(it)}`;
     };
 
-    var table = {
+    const table = {
       ws: literal,
       "ws-pea": wsPea,
       "ws-tpea": wsTPea,
       "line-comment": lineComment,
       "multiline-comment": multilineComment,
-      "interface": interface_,
-      operation: operation,
-      attribute: attribute,
-      dictionary: dictionary,
-      field: field,
-      exception: exception,
-      "const": const_,
-      typedef: typedef,
-      "implements": implements_,
-      callback: callback,
-      "enum": enum_,
-      iterable: iterable,
-      legacyiterable: legacyiterable,
-      maplike: maplike,
-      setlike: setlike,
+      interface: interface_,
+      "interface mixin": interface_mixin,
+      namespace,
+      operation,
+      attribute,
+      dictionary,
+      field,
+      const: const_,
+      typedef,
+      implements: implements_,
+      includes,
+      callback,
+      enum: enum_,
+      iterable,
+      legacyiterable,
+      maplike,
+      setlike,
       "callback interface": callbackInterface
     };
-    var dispatch = function(it) {
+    function dispatch(it) {
+      const dispatcher = table[it.type];
+      if (!dispatcher) {
+        throw new Error(`Type "${it.type}" is unsupported`)
+      }
       return table[it.type](it);
     };
-    var iterate = function(things) {
+    function iterate(things) {
       if (!things) return;
-      var ret = "";
-      for (var i = 0, n = things.length; i < n; i++) ret += dispatch(things[i]);
+      let ret = "";
+      for (const thing of things) ret += dispatch(thing);
       return ret;
     };
     return iterate(ast);
   };
 
 
-  var obj = {
-    write: function(ast, opt) {
-      if (!opt) opt = {};
-      return write(ast, opt);
-    }
+  const obj = {
+    write
   };
 
   if (typeof module !== 'undefined' && typeof module.exports !== 'undefined') {
     module.exports = obj;
   } else if (typeof define === 'function' && define.amd) {
-    define([], function() {
-      return obj;
-    });
+    define([], () => obj);
   } else {
     (self || window).WebIDL2Writer = obj;
   }
-}());
+})();
diff --git a/package-lock.json b/package-lock.json
index 53528713e57be6..a6f529d6c7f11d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,25 +1,52 @@
 {
   "name": "webidl2",
-  "version": "4.2.0",
+  "version": "10.2.1",
   "lockfileVersion": 1,
+  "requires": true,
   "dependencies": {
+    "@babel/code-frame": {
+      "version": "7.0.0-beta.40",
+      "resolved": "https://registry.npmjs.org/@babel/code-frame/-/code-frame-7.0.0-beta.40.tgz",
+      "integrity": "sha512-eVXQSbu/RimU6OKcK2/gDJVTFcxXJI4sHbIqw2mhwMZeQ2as/8AhS9DGkEDoHMBBNJZ5B0US63lF56x+KDcxiA==",
+      "dev": true,
+      "requires": {
+        "@babel/highlight": "7.0.0-beta.40"
+      }
+    },
+    "@babel/highlight": {
+      "version": "7.0.0-beta.40",
+      "resolved": "https://registry.npmjs.org/@babel/highlight/-/highlight-7.0.0-beta.40.tgz",
+      "integrity": "sha512-mOhhTrzieV6VO7odgzFGFapiwRK0ei8RZRhfzHhb6cpX3QM8XXuCLXWjN8qBB7JReDdUR80V3LFfFrGUYevhNg==",
+      "dev": true,
+      "requires": {
+        "chalk": "2.3.2",
+        "esutils": "2.0.2",
+        "js-tokens": "3.0.2"
+      }
+    },
     "ansi-regex": {
-      "version": "0.2.1",
-      "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-0.2.1.tgz",
-      "integrity": "sha1-DY6UaWej2BQ/k+JOKYUl/BsiNfk=",
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-3.0.0.tgz",
+      "integrity": "sha1-7QMXwyIGT3lGbAKWa922Bas32Zg=",
       "dev": true
     },
     "ansi-styles": {
-      "version": "1.1.0",
-      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-1.1.0.tgz",
-      "integrity": "sha1-6uy/Zs1waIJ2Cy9GkVgrj1XXp94=",
-      "dev": true
+      "version": "3.2.1",
+      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-3.2.1.tgz",
+      "integrity": "sha512-VT0ZI6kZRdTh8YyJw3SMbYm/u+NqfsAxEpWO0Pf9sq8/e94WxxOpPKx9FR1FlyCtOVDNOQ+8ntlqFxiRc+r5qA==",
+      "dev": true,
+      "requires": {
+        "color-convert": "1.9.1"
+      }
     },
     "arr-diff": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/arr-diff/-/arr-diff-2.0.0.tgz",
       "integrity": "sha1-jzuCf5Vai9ZpaX5KQlasPOrjVs8=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "arr-flatten": "1.1.0"
+      }
     },
     "arr-flatten": {
       "version": "1.1.0",
@@ -40,34 +67,51 @@
       "dev": true
     },
     "brace-expansion": {
-      "version": "1.1.8",
-      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-1.1.8.tgz",
-      "integrity": "sha1-wHshHHyVLsH479Uad+8NHTmQopI=",
-      "dev": true
+      "version": "1.1.11",
+      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-1.1.11.tgz",
+      "integrity": "sha512-iCuPHDFgrHX7H2vEI/5xpz07zSHB00TpugqhmYtVmMO6518mCuRMoOYFldEBl0g187ufozdaHgWKcYFb61qGiA==",
+      "dev": true,
+      "requires": {
+        "balanced-match": "1.0.0",
+        "concat-map": "0.0.1"
+      }
     },
     "braces": {
       "version": "1.8.5",
       "resolved": "https://registry.npmjs.org/braces/-/braces-1.8.5.tgz",
       "integrity": "sha1-uneWLhLf+WnWt2cR6RS3N4V79qc=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "expand-range": "1.8.2",
+        "preserve": "0.2.0",
+        "repeat-element": "1.1.2"
+      }
     },
     "browser-stdout": {
-      "version": "1.3.0",
-      "resolved": "https://registry.npmjs.org/browser-stdout/-/browser-stdout-1.3.0.tgz",
-      "integrity": "sha1-81HTKWnTL6XXpVZxVCY9korjvR8=",
+      "version": "1.3.1",
+      "resolved": "https://registry.npmjs.org/browser-stdout/-/browser-stdout-1.3.1.tgz",
+      "integrity": "sha512-qhAVI1+Av2X7qelOfAIYwXONood6XlZE/fXaBSmW/T5SzLAmCgzi+eiWE7fUvbHaeNBQH13UftjpXxsfLkMpgw==",
       "dev": true
     },
     "chalk": {
-      "version": "0.5.1",
-      "resolved": "https://registry.npmjs.org/chalk/-/chalk-0.5.1.tgz",
-      "integrity": "sha1-Zjs6ZItotV0EaQ1JFnqoN4WPIXQ=",
-      "dev": true
+      "version": "2.3.2",
+      "resolved": "https://registry.npmjs.org/chalk/-/chalk-2.3.2.tgz",
+      "integrity": "sha512-ZM4j2/ld/YZDc3Ma8PgN7gyAk+kHMMMyzLNryCPGhWrsfAuDVeuid5bpRFTDgMH9JBK2lA4dyyAkkZYF/WcqDQ==",
+      "dev": true,
+      "requires": {
+        "ansi-styles": "3.2.1",
+        "escape-string-regexp": "1.0.5",
+        "supports-color": "5.3.0"
+      }
     },
     "color-convert": {
-      "version": "1.9.0",
-      "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-1.9.0.tgz",
-      "integrity": "sha1-Gsz5fdc5uYO/mU1W/sj5WFNkG3o=",
-      "dev": true
+      "version": "1.9.1",
+      "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-1.9.1.tgz",
+      "integrity": "sha512-mjGanIiwQJskCC18rPR6OmrZ6fm2Lc7PeGFYwCmy5J34wC6F1PzdGL6xeMfmgicfYcNLGuVFA3WzXtIDCQSZxQ==",
+      "dev": true,
+      "requires": {
+        "color-name": "1.1.3"
+      }
     },
     "color-name": {
       "version": "1.1.3",
@@ -76,9 +120,9 @@
       "dev": true
     },
     "commander": {
-      "version": "2.9.0",
-      "resolved": "https://registry.npmjs.org/commander/-/commander-2.9.0.tgz",
-      "integrity": "sha1-nJkJQXbhIkDLItbFFGCYQA/g99Q=",
+      "version": "2.11.0",
+      "resolved": "https://registry.npmjs.org/commander/-/commander-2.11.0.tgz",
+      "integrity": "sha512-b0553uYA5YAEGgyYIGYROzKQ7X5RAqedkfjiZxwi0kL1g3bOaBNNZfYkzt/CL0umgD5wc9Jec2FbB98CjkMRvQ==",
       "dev": true
     },
     "concat-map": {
@@ -88,15 +132,24 @@
       "dev": true
     },
     "debug": {
-      "version": "2.6.0",
-      "resolved": "https://registry.npmjs.org/debug/-/debug-2.6.0.tgz",
-      "integrity": "sha1-vFlryr52F/Edn6FTYe3tVgi4SZs=",
-      "dev": true
+      "version": "3.1.0",
+      "resolved": "https://registry.npmjs.org/debug/-/debug-3.1.0.tgz",
+      "integrity": "sha512-OX8XqP7/1a9cqkxYw2yXss15f26NKWBpDXQd0/uK/KPqdQhxbPa994hnzjcE2VqQpDslf55723cKPUOGSmMY3g==",
+      "dev": true,
+      "requires": {
+        "ms": "2.0.0"
+      }
     },
     "diff": {
-      "version": "3.2.0",
-      "resolved": "https://registry.npmjs.org/diff/-/diff-3.2.0.tgz",
-      "integrity": "sha1-yc45Okt8vQsFinJck98pkCeGj/k=",
+      "version": "3.5.0",
+      "resolved": "https://registry.npmjs.org/diff/-/diff-3.5.0.tgz",
+      "integrity": "sha512-A46qtFgd+g7pDZinpnwiRJtxbC1hpgf0uzP3iG89scHk0AUC7A1TGxf5OiiOUv/JMZR8GOt8hL900hV0bOy5xA==",
+      "dev": true
+    },
+    "diff-match-patch": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/diff-match-patch/-/diff-match-patch-1.0.0.tgz",
+      "integrity": "sha1-HMPIOkkNZ/ldkeOfatHy4Ia2MEg=",
       "dev": true
     },
     "escape-string-regexp": {
@@ -105,37 +158,52 @@
       "integrity": "sha1-G2HAViGQqN/2rjuyzwIAyhMLhtQ=",
       "dev": true
     },
+    "esutils": {
+      "version": "2.0.2",
+      "resolved": "https://registry.npmjs.org/esutils/-/esutils-2.0.2.tgz",
+      "integrity": "sha1-Cr9PHKpbyx96nYrMbepPqqBLrJs=",
+      "dev": true
+    },
     "expand-brackets": {
       "version": "0.1.5",
       "resolved": "https://registry.npmjs.org/expand-brackets/-/expand-brackets-0.1.5.tgz",
       "integrity": "sha1-3wcoTjQqgHzXM6xa9yQR5YHRF3s=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "is-posix-bracket": "0.1.1"
+      }
     },
     "expand-range": {
       "version": "1.8.2",
       "resolved": "https://registry.npmjs.org/expand-range/-/expand-range-1.8.2.tgz",
       "integrity": "sha1-opnv/TNf4nIeuujiV+x5ZE/IUzc=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "fill-range": "2.2.3"
+      }
     },
     "expect": {
-      "version": "21.2.1",
-      "resolved": "https://registry.npmjs.org/expect/-/expect-21.2.1.tgz",
-      "integrity": "sha512-orfQQqFRTX0jH7znRIGi8ZMR8kTNpXklTTz8+HGTpmTKZo3Occ6JNB5FXMb8cRuiiC/GyDqsr30zUa66ACYlYw==",
+      "version": "22.4.0",
+      "resolved": "https://registry.npmjs.org/expect/-/expect-22.4.0.tgz",
+      "integrity": "sha512-Fiy862jT3qc70hwIHwwCBNISmaqBrfWKKrtqyMJ6iwZr+6KXtcnHojZFtd63TPRvRl8EQTJ+YXYy2lK6/6u+Hw==",
       "dev": true,
-      "dependencies": {
-        "ansi-styles": {
-          "version": "3.2.0",
-          "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-3.2.0.tgz",
-          "integrity": "sha512-NnSOmMEYtVR2JVMIGTzynRkkaxtiq1xnFBcdQD/DnNCYPoEPsVJhM98BDyaoNOQIi7p4okdi3E27eN7GQbsUug==",
-          "dev": true
-        }
+      "requires": {
+        "ansi-styles": "3.2.1",
+        "jest-diff": "22.4.0",
+        "jest-get-type": "22.1.0",
+        "jest-matcher-utils": "22.4.0",
+        "jest-message-util": "22.4.0",
+        "jest-regex-util": "22.1.0"
       }
     },
     "extglob": {
       "version": "0.3.2",
       "resolved": "https://registry.npmjs.org/extglob/-/extglob-0.3.2.tgz",
       "integrity": "sha1-Lhj/PS9JqydlzskCPwEdqo2DSaE=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "is-extglob": "1.0.0"
+      }
     },
     "filename-regex": {
       "version": "2.0.1",
@@ -147,7 +215,14 @@
       "version": "2.2.3",
       "resolved": "https://registry.npmjs.org/fill-range/-/fill-range-2.2.3.tgz",
       "integrity": "sha1-ULd9/X5Gm8dJJHCWNpn+eoSFpyM=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "is-number": "2.1.0",
+        "isobject": "2.1.0",
+        "randomatic": "1.1.7",
+        "repeat-element": "1.1.2",
+        "repeat-string": "1.6.1"
+      }
     },
     "for-in": {
       "version": "1.0.2",
@@ -159,7 +234,10 @@
       "version": "0.1.5",
       "resolved": "https://registry.npmjs.org/for-own/-/for-own-0.1.5.tgz",
       "integrity": "sha1-UmXGgaTylNq78XyVCbZ2OqhFEM4=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "for-in": "1.0.2"
+      }
     },
     "fs.realpath": {
       "version": "1.0.0",
@@ -168,52 +246,65 @@
       "dev": true
     },
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+        "browser-stdout": "1.3.1",
+        "commander": "2.11.0",
+        "debug": "3.1.0",
+        "diff": "3.5.0",
+        "escape-string-regexp": "1.0.5",
+        "glob": "7.1.2",
+        "growl": "1.10.3",
+        "he": "1.1.1",
+        "mkdirp": "0.5.1",
+        "supports-color": "4.4.0"
+      },
       "dependencies": {
-        "supports-color": {
-          "version": "3.1.2",
-          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-3.1.2.tgz",
-          "integrity": "sha1-cqJiiU2dQIuVbKBf83su2KbiotU=",
+        "has-flag": {
+          "version": "2.0.0",
+          "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-2.0.0.tgz",
+          "integrity": "sha1-6CB68cx7MNRGzHC3NLXovhj4jVE=",
           "dev": true
+        },
+        "supports-color": {
+          "version": "4.4.0",
+          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-4.4.0.tgz",
+          "integrity": "sha512-rKC3+DyXWgK0ZLKwmRsrkyHVZAjNkfzeehuFWdGGcqGDTZFH73+RH6S/RDAAxl9GusSjZSUWYLmT9N5pzXFOXQ==",
+          "dev": true,
+          "requires": {
+            "has-flag": "2.0.0"
+          }
         }
       }
     },
     "ms": {
-      "version": "0.7.2",
-      "resolved": "https://registry.npmjs.org/ms/-/ms-0.7.2.tgz",
-      "integrity": "sha1-riXPJRKziFodldfwN4aNhDESR2U=",
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/ms/-/ms-2.0.0.tgz",
+      "integrity": "sha1-VgiurfwAvmwpAd9fmGF4jeDVl8g=",
       "dev": true
     },
     "normalize-path": {
       "version": "2.1.1",
       "resolved": "https://registry.npmjs.org/normalize-path/-/normalize-path-2.1.1.tgz",
       "integrity": "sha1-GrKLVW4Zg2Oowab35vogE3/mrtk=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "remove-trailing-separator": "1.1.0"
+      }
     },
     "object.omit": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/object.omit/-/object.omit-2.0.1.tgz",
       "integrity": "sha1-Gpx0SCnznbuFjHbKNXmuKlTr0fo=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "for-own": "0.1.5",
+        "is-extendable": "0.1.1"
+      }
     },
     "once": {
       "version": "1.4.0",
       "resolved": "https://registry.npmjs.org/once/-/once-1.4.0.tgz",
       "integrity": "sha1-WDsap3WWHUsROsF9nFC6753Xa9E=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "wrappy": "1.0.2"
+      }
     },
     "parse-glob": {
       "version": "3.0.4",
       "resolved": "https://registry.npmjs.org/parse-glob/-/parse-glob-3.0.4.tgz",
       "integrity": "sha1-ssN2z7EfNVE7rdFz7wu246OIORw=",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "glob-base": "0.3.0",
+        "is-dotfile": "1.0.3",
+        "is-extglob": "1.0.0",
+        "is-glob": "2.0.1"
+      }
     },
     "path-is-absolute": {
       "version": "1.0.1",
@@ -548,23 +602,13 @@
       "dev": true
     },
     "pretty-format": {
-      "version": "21.2.1",
-      "resolved": "https://registry.npmjs.org/pretty-format/-/pretty-format-21.2.1.tgz",
-      "integrity": "sha512-ZdWPGYAnYfcVP8yKA3zFjCn8s4/17TeYH28MXuC8vTp0o21eXjbFGcOAXZEaDaOFJjc3h2qa7HQNHNshhvoh2A==",
+      "version": "22.4.0",
+      "resolved": "https://registry.npmjs.org/pretty-format/-/pretty-format-22.4.0.tgz",
+      "integrity": "sha512-pvCxP2iODIIk9adXlo4S3GRj0BrJiil68kByAa1PrgG97c1tClh9dLMgp3Z6cHFZrclaABt0UH8PIhwHuFLqYA==",
       "dev": true,
-      "dependencies": {
-        "ansi-regex": {
-          "version": "3.0.0",
-          "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-3.0.0.tgz",
-          "integrity": "sha1-7QMXwyIGT3lGbAKWa922Bas32Zg=",
-          "dev": true
-        },
-        "ansi-styles": {
-          "version": "3.2.0",
-          "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-3.2.0.tgz",
-          "integrity": "sha512-NnSOmMEYtVR2JVMIGTzynRkkaxtiq1xnFBcdQD/DnNCYPoEPsVJhM98BDyaoNOQIi7p4okdi3E27eN7GQbsUug==",
-          "dev": true
-        }
+      "requires": {
+        "ansi-regex": "3.0.0",
+        "ansi-styles": "3.2.1"
       }
     },
     "randomatic": {
@@ -572,18 +616,28 @@
       "resolved": "https://registry.npmjs.org/randomatic/-/randomatic-1.1.7.tgz",
       "integrity": "sha512-D5JUjPyJbaJDkuAazpVnSfVkLlpeO3wDlPROTMLGKG1zMFNFRgrciKo1ltz/AzNTkqE0HzDx655QOL51N06how==",
       "dev": true,
+      "requires": {
+        "is-number": "3.0.0",
+        "kind-of": "4.0.0"
+      },
       "dependencies": {
         "is-number": {
           "version": "3.0.0",
           "resolved": "https://registry.npmjs.org/is-number/-/is-number-3.0.0.tgz",
           "integrity": "sha1-JP1iAaR4LPUFYcgQJ2r8fRLXEZU=",
           "dev": true,
+          "requires": {
+            "kind-of": "3.2.2"
+          },
           "dependencies": {
             "kind-of": {
               "version": "3.2.2",
               "resolved": "https://registry.npmjs.org/kind-of/-/kind-of-3.2.2.tgz",
               "integrity": "sha1-MeohpzS6ubuw8yRm2JOupR5KPGQ=",
-              "dev": true
+              "dev": true,
+              "requires": {
+                "is-buffer": "1.1.6"
+              }
             }
           }
         },
@@ -591,7 +645,10 @@
           "version": "4.0.0",
           "resolved": "https://registry.npmjs.org/kind-of/-/kind-of-4.0.0.tgz",
           "integrity": "sha1-IIE989cSkosgc3hpGkUGb65y3Vc=",
-          "dev": true
+          "dev": true,
+          "requires": {
+            "is-buffer": "1.1.6"
+          }
         }
       }
     },
@@ -599,7 +656,10 @@
       "version": "0.4.4",
       "resolved": "https://registry.npmjs.org/regex-cache/-/regex-cache-0.4.4.tgz",
       "integrity": "sha512-nVIZwtCjkC9YgvWkpM55B5rBhBYRZhAaJbgcFYXXsHnbZ9UZI9nnVWYZpBlCqv9ho2eZryPnWrZGsOdPwVWXWQ==",
-      "dev": true
+      "dev": true,
+      "requires": {
+        "is-equal-shallow": "0.1.3"
+      }
     },
     "remove-trailing-separator": {
       "version": "1.1.0",
@@ -625,17 +685,20 @@
       "integrity": "sha1-xB8vbDn8FtHNF61LXYlhFK5HDVU=",
       "dev": true
     },
-    "strip-ansi": {
-      "version": "0.3.0",
-      "resolved": "https://registry.npmjs.org/strip-ansi/-/strip-ansi-0.3.0.tgz",
-      "integrity": "sha1-JfSOoiynkYfzF0pNuHWTR7sSYiA=",
+    "stack-utils": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/stack-utils/-/stack-utils-1.0.1.tgz",
+      "integrity": "sha1-1PM6tU6OOHeLDKXP07OvsS22hiA=",
       "dev": true
     },
     "supports-color": {
-      "version": "0.2.0",
-      "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-0.2.0.tgz",
-      "integrity": "sha1-2S3iaU6z9nMjlz1649i1W0wiGQo=",
-      "dev": true
+      "version": "5.3.0",
+      "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.3.0.tgz",
+      "integrity": "sha512-0aP01LLIskjKs3lq52EC0aGBAJhLq7B2Rd8HC/DR/PtNNpcLilNmHC12O+hu0usQpo7wtHNRqtrhBwtDb0+dNg==",
+      "dev": true,
+      "requires": {
+        "has-flag": "3.0.0"
+      }
     },
     "wrappy": {
       "version": "1.0.2",
diff --git a/package.json b/package.json
index d7b8a421241f85..ab282d189bb9e5 100644
--- a/package.json
+++ b/package.json
@@ -1,22 +1,24 @@
 {
   "name": "webidl2",
   "description": "A WebIDL Parser",
-  "version": "8.1.0",
+  "version": "10.2.1",
   "contributors": [
     "Robin Berjon <robin@berjon.com> (https://berjon.com)",
     "Marcos Caceres <marcos@marcosc.com> (https://marcosc.com)",
-    "Kagami Sascha Rosylight <saschaplas@outlook.com>"
+    "Kagami Sascha Rosylight <saschaplas@outlook.com>",
+    "Timothy Gu <timothygu99@gmail.com>"
   ],
   "license": "W3C",
   "dependencies": {},
   "devDependencies": {
-    "expect": "21.2.1",
-    "jsondiffpatch": "0.2.5",
-    "mocha": "4.0.1"
+    "expect": "22.4.0",
+    "jsondiffpatch": "0.3.5",
+    "mocha": "5.0.4"
   },
   "scripts": {
-    "test": "mocha"
+    "test": "mocha",
+    "acquire": "node test/util/acquire.js"
   },
-  "repository": "git://github.com/darobin/webidl2.js",
+  "repository": "git://github.com/w3c/webidl2.js",
   "main": "index"
 }
diff --git a/test/invalid.js b/test/invalid.js
index 548f0ea4b3d4ef..19bbf006e579ef 100644
--- a/test/invalid.js
+++ b/test/invalid.js
@@ -4,37 +4,17 @@
 
 "use strict";
 
-const wp = require("../lib/webidl2");
-const expect = require("expect");
-const pth = require("path");
+const { collect } = require("./util/collect");
 const fs = require("fs");
+const expect = require("expect");
 
 describe("Parses all of the invalid IDLs to check that they blow up correctly", () => {
-  const dir = pth.join(__dirname, "invalid/idl");
-  const skip = {};
-  const idls = fs.readdirSync(dir)
-    .filter(it => (/\.w?idl$/).test(it) && !skip[it])
-    .map(it => pth.join(dir, it));
-  const errors = idls.map(it => pth.join(__dirname, "invalid", "json", pth.basename(it).replace(/\.w?idl/, ".json")));
-
-  for (let i = 0, n = idls.length; i < n; i++) {
-    const idl = idls[i];
-    const err = JSON.parse(fs.readFileSync(errors[i], "utf8"));
-
-    it(`should produce the right error for ${idl}`, () => {
-      let error;
-      try {
-        var ast = wp.parse(fs.readFileSync(idl, "utf8"));
-        console.log(JSON.stringify(ast, null, 4));
-      }
-      catch (e) {
-        error = e;
-      }
-      finally {
-        expect(error).toBeTruthy();
-        expect(error.message).toEqual(err.message);
-        expect(error.line).toEqual(err.line);
-      }
+  for (const test of collect("invalid", { expectError: true })) {
+    it(`should produce the right error for ${test.path}`, () => {
+      const err = test.readJSON();
+      expect(test.error).toBeTruthy();
+      expect(test.error.message).toEqual(err.message);
+      expect(test.error.line).toEqual(err.line);
     });
   }
 });
diff --git a/test/syntax/idl/iterator.widl b/test/invalid/idl/iterator.widl
similarity index 100%
rename from test/syntax/idl/iterator.widl
rename to test/invalid/idl/iterator.widl
diff --git a/test/invalid/idl/no-semicolon-callback.widl b/test/invalid/idl/no-semicolon-callback.widl
new file mode 100644
index 00000000000000..cb2055718e5f04
--- /dev/null
+++ b/test/invalid/idl/no-semicolon-callback.widl
@@ -0,0 +1,7 @@
+callback interface NoSemicolon {
+  attribute boolean noSemiColon;
+}
+
+enum YouNeedOne {
+  "really"
+}
diff --git a/test/invalid/idl/no-semicolon.widl b/test/invalid/idl/no-semicolon.widl
new file mode 100644
index 00000000000000..10bc716249b3e1
--- /dev/null
+++ b/test/invalid/idl/no-semicolon.widl
@@ -0,0 +1,7 @@
+partial interface NoSemicolon {
+  attribute boolean noSemiColon;
+}
+
+enum YouNeedOne {
+  "really"
+}
diff --git a/test/invalid/idl/stray-slash.widl b/test/invalid/idl/stray-slash.widl
new file mode 100644
index 00000000000000..b673aa94b01d65
--- /dev/null
+++ b/test/invalid/idl/stray-slash.widl
@@ -0,0 +1,2 @@
+// This is a comment.
+/ This is not.
diff --git a/test/invalid/idl/stringconstants.idl b/test/invalid/idl/stringconstants.widl
similarity index 100%
rename from test/invalid/idl/stringconstants.idl
rename to test/invalid/idl/stringconstants.widl
diff --git a/test/invalid/json/array.json b/test/invalid/json/array.json
index 30b377fc71c859..898b2d836bff81 100644
--- a/test/invalid/json/array.json
+++ b/test/invalid/json/array.json
@@ -1,4 +1,4 @@
 {
-    "message": "No name in attribute",
+    "message": "Got an error during or right after parsing `interface LotteryResults`: No name in attribute",
     "line": 5
-}
\ No newline at end of file
+}
diff --git a/test/invalid/json/caller.json b/test/invalid/json/caller.json
index 79b8ecac04f3a3..567fa3368129f9 100644
--- a/test/invalid/json/caller.json
+++ b/test/invalid/json/caller.json
@@ -1,4 +1,4 @@
 {
-    "message": "Invalid operation",
+    "message": "Got an error during or right after parsing `interface NumberQuadrupler`: Invalid operation",
     "line": 6
 }
diff --git a/test/invalid/json/dict-required-default.json b/test/invalid/json/dict-required-default.json
index c5afeca85c05de..82b6b2ae42a6f6 100644
--- a/test/invalid/json/dict-required-default.json
+++ b/test/invalid/json/dict-required-default.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Required member must not have a default"
+    "message":  "Got an error during or right after parsing `dictionary Dict`: Required member must not have a default"
 ,   "line":     4
 }
diff --git a/test/invalid/json/duplicate.json b/test/invalid/json/duplicate.json
index cef335875c391f..e88a7156fe8c1c 100644
--- a/test/invalid/json/duplicate.json
+++ b/test/invalid/json/duplicate.json
@@ -1,4 +1,4 @@
 {
-    "message": "The name \"Test\" of type \"typedef\" is already seen",
+    "message": "Got an error during or right after parsing `typedef Test`: The name \"Test\" of type \"typedef\" is already seen",
     "line": 3
-}
\ No newline at end of file
+}
diff --git a/test/invalid/json/enum.json b/test/invalid/json/enum.json
index 166115801c3411..073ff6c290cafd 100644
--- a/test/invalid/json/enum.json
+++ b/test/invalid/json/enum.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Unexpected value in enum"
+    "message":  "Got an error during or right after parsing `enum foo`: Unexpected value in enum"
 ,   "line":     1
 }
diff --git a/test/invalid/json/exception.json b/test/invalid/json/exception.json
index f52cda13837c5a..ad9fac6ca2f64e 100644
--- a/test/invalid/json/exception.json
+++ b/test/invalid/json/exception.json
@@ -1,4 +1,4 @@
 {
-    "message": "Unrecognised tokens",
+    "message": "Got an error before parsing any named definition: Unrecognised tokens",
     "line": 4
 }
diff --git a/test/invalid/json/iterator.json b/test/invalid/json/iterator.json
new file mode 100644
index 00000000000000..e46d653ae3c512
--- /dev/null
+++ b/test/invalid/json/iterator.json
@@ -0,0 +1,4 @@
+{
+    "message": "Got an error during or right after parsing `interface SessionManager`: Invalid operation",
+    "line": 5
+}
diff --git a/test/invalid/json/maplike-1type.json b/test/invalid/json/maplike-1type.json
index 859a820a4910cd..75e7a35ee256e9 100644
--- a/test/invalid/json/maplike-1type.json
+++ b/test/invalid/json/maplike-1type.json
@@ -1,4 +1,4 @@
 {
-    "message": "Missing second type argument in maplike declaration",
+    "message": "Got an error during or right after parsing `interface MapLikeOneType`: Missing second type argument in maplike declaration",
     "line": 2
-}
\ No newline at end of file
+}
diff --git a/test/invalid/json/module.json b/test/invalid/json/module.json
index 3b0984d973f45e..9c071cdd07a7a3 100644
--- a/test/invalid/json/module.json
+++ b/test/invalid/json/module.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Unrecognised tokens"
+    "message":  "Got an error before parsing any named definition: Unrecognised tokens"
 ,   "line":     2
 }
diff --git a/test/invalid/json/no-semicolon-callback.json b/test/invalid/json/no-semicolon-callback.json
new file mode 100644
index 00000000000000..1db9d14c8e2c51
--- /dev/null
+++ b/test/invalid/json/no-semicolon-callback.json
@@ -0,0 +1,4 @@
+{
+    "message": "Got an error during or right after parsing `callback interface NoSemicolon`: Missing semicolon after interface",
+    "line": 5
+}
diff --git a/test/invalid/json/no-semicolon.json b/test/invalid/json/no-semicolon.json
new file mode 100644
index 00000000000000..087532a012f592
--- /dev/null
+++ b/test/invalid/json/no-semicolon.json
@@ -0,0 +1,4 @@
+{
+    "message": "Got an error during or right after parsing `partial interface NoSemicolon`: Missing semicolon after interface",
+    "line": 5
+}
diff --git a/test/invalid/json/nonnullableany.json b/test/invalid/json/nonnullableany.json
index cf5229e8e44ab0..8a1f90046ae4d9 100644
--- a/test/invalid/json/nonnullableany.json
+++ b/test/invalid/json/nonnullableany.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Type any cannot be made nullable"
+    "message":  "Got an error during or right after parsing `interface NonNullable`: Type any cannot be made nullable"
 ,   "line":     2
 }
diff --git a/test/invalid/json/nonnullableobjects.json b/test/invalid/json/nonnullableobjects.json
index 23cbb3e5d180f1..52bd8dac16fe69 100644
--- a/test/invalid/json/nonnullableobjects.json
+++ b/test/invalid/json/nonnullableobjects.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Can't nullable more than once"
+    "message":  "Got an error during or right after parsing `interface NonNullable`: Can't nullable more than once"
 ,   "line":     4
 }
diff --git a/test/invalid/json/promise-with-extended-attribute.json b/test/invalid/json/promise-with-extended-attribute.json
index e9623ce7cc8c58..71212d46e3c011 100644
--- a/test/invalid/json/promise-with-extended-attribute.json
+++ b/test/invalid/json/promise-with-extended-attribute.json
@@ -1,4 +1,4 @@
 {
-    "message": "Promise type cannot have extended attribute",
+    "message": "Got an error during or right after parsing `interface Foo`: Promise type cannot have extended attribute",
     "line": 2
 }
diff --git a/test/invalid/json/raises.json b/test/invalid/json/raises.json
index 8b67afe4fc9702..3165b874f0c189 100644
--- a/test/invalid/json/raises.json
+++ b/test/invalid/json/raises.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Unterminated attribute"
+    "message":  "Got an error during or right after parsing `interface Person`: Unterminated attribute"
 ,   "line":     5
 }
diff --git a/test/invalid/json/readonly-iterable.json b/test/invalid/json/readonly-iterable.json
index c6f52a24615883..1a09264a6d0d65 100644
--- a/test/invalid/json/readonly-iterable.json
+++ b/test/invalid/json/readonly-iterable.json
@@ -1,4 +1,4 @@
 {
-    "message": "Invalid operation",
+    "message": "Got an error during or right after parsing `interface ReadonlyIterable`: Invalid operation",
     "line": 2
-}
\ No newline at end of file
+}
diff --git a/test/invalid/json/record-key-with-extended-attribute.json b/test/invalid/json/record-key-with-extended-attribute.json
index 3945825c318d61..4002e7fe0155d5 100644
--- a/test/invalid/json/record-key-with-extended-attribute.json
+++ b/test/invalid/json/record-key-with-extended-attribute.json
@@ -1,4 +1,4 @@
 {
-    "message": "Record key cannot have extended attribute",
+    "message": "Got an error during or right after parsing `interface Foo`: Record key cannot have extended attribute",
     "line": 2
 }
diff --git a/test/invalid/json/record-key.json b/test/invalid/json/record-key.json
index 3b929b926a30a7..179d645d6a753d 100644
--- a/test/invalid/json/record-key.json
+++ b/test/invalid/json/record-key.json
@@ -1,4 +1,4 @@
 {
-    "message": "Record key must be DOMString, USVString, or ByteString",
+    "message": "Got an error during or right after parsing `interface Foo`: Record key must be DOMString, USVString, or ByteString",
     "line": 2
 }
diff --git a/test/invalid/json/scopedname.json b/test/invalid/json/scopedname.json
index 8e2cd803287ef4..4620d2df5fa0cc 100644
--- a/test/invalid/json/scopedname.json
+++ b/test/invalid/json/scopedname.json
@@ -1,4 +1,4 @@
 {
-    "message":  "No name in typedef"
+    "message":  "Got an error before parsing any named definition: No name in typedef"
 ,   "line":     2
 }
diff --git a/test/invalid/json/sequenceAsAttribute.json b/test/invalid/json/sequenceAsAttribute.json
index b714f5d92434a2..5b4314a6de128d 100644
--- a/test/invalid/json/sequenceAsAttribute.json
+++ b/test/invalid/json/sequenceAsAttribute.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Attributes cannot accept sequence types"
+    "message":  "Got an error during or right after parsing `interface sequenceAsAttribute`: Attributes cannot accept sequence types"
 ,   "line":     2
 }
diff --git a/test/invalid/json/setlike-2types.json b/test/invalid/json/setlike-2types.json
index c9e49b6756d5d9..2900e1bac30074 100644
--- a/test/invalid/json/setlike-2types.json
+++ b/test/invalid/json/setlike-2types.json
@@ -1,4 +1,4 @@
 {
-    "message": "Unterminated setlike declaration",
+    "message": "Got an error during or right after parsing `interface SetLikeTwoTypes`: Unterminated setlike declaration",
     "line": 2
-}
\ No newline at end of file
+}
diff --git a/test/invalid/json/setter-creator.json b/test/invalid/json/setter-creator.json
index 07b9f1f4bc42c4..25decb374e12fe 100644
--- a/test/invalid/json/setter-creator.json
+++ b/test/invalid/json/setter-creator.json
@@ -1,4 +1,4 @@
 {
-    "message": "Invalid operation",
+    "message": "Got an error during or right after parsing `interface OrderedMap`: Invalid operation",
     "line": 3
 }
diff --git a/test/invalid/json/special-omittable.json b/test/invalid/json/special-omittable.json
index 7acb08834b0e6e..c20b28e03c17d6 100644
--- a/test/invalid/json/special-omittable.json
+++ b/test/invalid/json/special-omittable.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Invalid operation"
+    "message":  "Got an error during or right after parsing `interface Dictionary`: Invalid operation"
 ,   "line":     6
 }
diff --git a/test/invalid/json/stray-slash.json b/test/invalid/json/stray-slash.json
new file mode 100644
index 00000000000000..9c071cdd07a7a3
--- /dev/null
+++ b/test/invalid/json/stray-slash.json
@@ -0,0 +1,4 @@
+{
+    "message":  "Got an error before parsing any named definition: Unrecognised tokens"
+,   "line":     2
+}
diff --git a/test/invalid/json/stringconstants.json b/test/invalid/json/stringconstants.json
index d5bf1a8832c664..1eeb31cd3ef802 100644
--- a/test/invalid/json/stringconstants.json
+++ b/test/invalid/json/stringconstants.json
@@ -1,4 +1,4 @@
 {
-    "message":  "No value for const"
+    "message":  "Got an error during or right after parsing `interface Util`: No value for const"
 ,   "line":     2
 }
diff --git a/test/invalid/json/typedef-nested.json b/test/invalid/json/typedef-nested.json
index d7fb9182f86e9d..8c6081496851ab 100644
--- a/test/invalid/json/typedef-nested.json
+++ b/test/invalid/json/typedef-nested.json
@@ -1,4 +1,4 @@
 {
-    "message":  "Invalid operation"
+    "message":  "Got an error during or right after parsing `interface Widget`: Invalid operation"
 ,   "line":     14
-}
\ No newline at end of file
+}
diff --git a/test/syntax.js b/test/syntax.js
index 0838f350cd96c9..05d647eda10394 100644
--- a/test/syntax.js
+++ b/test/syntax.js
@@ -1,34 +1,14 @@
 "use strict";
 
-const wp = require("../lib/webidl2");
+const { collect } = require("./util/collect");
 const expect = require("expect");
-const pth = require("path");
-const fs = require("fs");
-const jdp = require("jsondiffpatch");
 const debug = true;
 
 describe("Parses all of the IDLs to produce the correct ASTs", () => {
-  const dir = pth.join(__dirname, "syntax/idl");
-  const skip = {}; // use if we have a broken test
-  const idls = fs.readdirSync(dir)
-    .filter(it => (/\.widl$/).test(it) && !skip[it])
-    .map(it => pth.join(dir, it));
-  const jsons = idls.map(it => pth.join(__dirname, "syntax/json", pth.basename(it).replace(".widl", ".json")));
-
-  for (let i = 0, n = idls.length; i < n; i++) {
-    const idl = idls[i];
-    const json = jsons[i];
-
-    it(`should produce the same AST for ${idl}`, () => {
+  for (const test of collect("syntax")) {
+    it(`should produce the same AST for ${test.path}`, () => {
       try {
-        const optFile = pth.join(__dirname, "syntax/opt", pth.basename(json));
-        let opt = undefined;
-        if (fs.existsSync(optFile))
-          opt = JSON.parse(fs.readFileSync(optFile, "utf8"));
-        const diff = jdp.diff(JSON.parse(fs.readFileSync(json, "utf8")),
-          wp.parse(fs.readFileSync(idl, "utf8").replace(/\r\n/g, "\n"), opt));
-        if (diff && debug) console.log(JSON.stringify(diff, null, 4));
-        expect(diff).toBe(undefined);
+        expect(test.diff()).toBeFalsy();
       }
       catch (e) {
         console.log(e.toString());
diff --git a/test/syntax/idl/extended-attributes.widl b/test/syntax/idl/extended-attributes.widl
index a49463b3d76339..57d4f97de7c317 100644
--- a/test/syntax/idl/extended-attributes.widl
+++ b/test/syntax/idl/extended-attributes.widl
@@ -20,4 +20,10 @@ interface Circle {
   attribute double cx;
   attribute double cy;
   readonly attribute double circumference;
-};
\ No newline at end of file
+};
+
+// Extracted from https://heycam.github.io/webidl/#idl-annotated-types on 2017-12-15
+[Exposed=Window]
+interface I {
+    attribute [XAttr] (long or Node) attrib;
+};
diff --git a/test/syntax/idl/typedef-union.idl b/test/syntax/idl/typedef-union.widl
similarity index 100%
rename from test/syntax/idl/typedef-union.idl
rename to test/syntax/idl/typedef-union.widl
diff --git a/test/syntax/json/allowany.json b/test/syntax/json/allowany.json
index ee898d68296c1d..cd5c6e00ac33b2 100644
--- a/test/syntax/json/allowany.json
+++ b/test/syntax/json/allowany.json
@@ -12,6 +12,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -30,6 +31,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -43,6 +45,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -62,6 +65,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -82,6 +86,7 @@
                             }
                         ],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/attributes.json b/test/syntax/json/attributes.json
index 86fe9d52dec69b..c90c70d7edc4ca 100644
--- a/test/syntax/json/attributes.json
+++ b/test/syntax/json/attributes.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -24,4 +25,4 @@
         "inheritance": null,
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/callback.json b/test/syntax/json/callback.json
index 5301c40d754b94..f31067dd25cb99 100644
--- a/test/syntax/json/callback.json
+++ b/test/syntax/json/callback.json
@@ -3,6 +3,7 @@
         "type": "callback",
         "name": "AsyncOperationCallback",
         "idlType": {
+            "type": "return-type",
             "sequence": false,
             "generic": null,
             "nullable": false,
@@ -15,6 +16,7 @@
                 "variadic": false,
                 "extAttrs": [],
                 "idlType": {
+                    "type": "argument-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -39,6 +41,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -52,6 +55,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -71,6 +75,7 @@
         "type": "callback",
         "name": "SortCallback",
         "idlType": {
+            "type": "return-type",
             "sequence": false,
             "generic": null,
             "nullable": false,
@@ -83,6 +88,7 @@
                 "variadic": false,
                 "extAttrs": [],
                 "idlType": {
+                    "type": "argument-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -96,6 +102,7 @@
                 "variadic": false,
                 "extAttrs": [],
                 "idlType": {
+                    "type": "argument-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
diff --git a/test/syntax/json/constants.json b/test/syntax/json/constants.json
index 75222866443f6c..4b98751622c339 100644
--- a/test/syntax/json/constants.json
+++ b/test/syntax/json/constants.json
@@ -7,7 +7,10 @@
             {
                 "type": "const",
                 "nullable": false,
-                "idlType": "boolean",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "boolean"
+                },
                 "name": "DEBUG",
                 "value": {
                     "type": "boolean",
@@ -18,7 +21,10 @@
             {
                 "type": "const",
                 "nullable": false,
-                "idlType": "short",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "short"
+                },
                 "name": "negative",
                 "value": {
                     "type": "number",
@@ -29,7 +35,10 @@
             {
                 "type": "const",
                 "nullable": false,
-                "idlType": "octet",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "octet"
+                },
                 "name": "LF",
                 "value": {
                     "type": "number",
@@ -40,7 +49,10 @@
             {
                 "type": "const",
                 "nullable": false,
-                "idlType": "unsigned long",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "unsigned long"
+                },
                 "name": "BIT_MASK",
                 "value": {
                     "type": "number",
@@ -51,7 +63,10 @@
             {
                 "type": "const",
                 "nullable": false,
-                "idlType": "float",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "float"
+                },
                 "name": "AVOGADRO",
                 "value": {
                     "type": "number",
@@ -62,7 +77,10 @@
             {
                 "type": "const",
                 "nullable": false,
-                "idlType": "unrestricted float",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "unrestricted float"
+                },
                 "name": "sobig",
                 "value": {
                     "type": "Infinity",
@@ -73,7 +91,10 @@
             {
                 "type": "const",
                 "nullable": false,
-                "idlType": "unrestricted double",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "unrestricted double"
+                },
                 "name": "minusonedividedbyzero",
                 "value": {
                     "type": "Infinity",
@@ -84,7 +105,10 @@
             {
                 "type": "const",
                 "nullable": false,
-                "idlType": "short",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "short"
+                },
                 "name": "notanumber",
                 "value": {
                     "type": "NaN"
@@ -95,4 +119,4 @@
         "inheritance": null,
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/constructor.json b/test/syntax/json/constructor.json
index ee55ef03e144ab..292236f291bd9b 100644
--- a/test/syntax/json/constructor.json
+++ b/test/syntax/json/constructor.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -27,6 +28,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -43,6 +45,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -59,6 +62,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -85,6 +89,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/dictionary-inherits.json b/test/syntax/json/dictionary-inherits.json
index ef30b1ab76d565..9b928f4f0a6f22 100644
--- a/test/syntax/json/dictionary-inherits.json
+++ b/test/syntax/json/dictionary-inherits.json
@@ -9,6 +9,7 @@
                 "name": "fillPattern",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": true,
@@ -26,6 +27,7 @@
                 "name": "strokePattern",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": true,
@@ -42,6 +44,7 @@
                 "name": "position",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -64,6 +67,7 @@
                 "name": "hydrometry",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -76,4 +80,4 @@
         "inheritance": "PaintOptions",
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/dictionary.json b/test/syntax/json/dictionary.json
index 28494ce437c7bb..f74fedc3d35b86 100644
--- a/test/syntax/json/dictionary.json
+++ b/test/syntax/json/dictionary.json
@@ -9,6 +9,7 @@
                 "name": "fillPattern",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": true,
@@ -26,6 +27,7 @@
                 "name": "strokePattern",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": true,
@@ -42,6 +44,7 @@
                 "name": "position",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -55,11 +58,13 @@
                 "name": "seq",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": true,
                     "generic": "sequence",
                     "nullable": false,
                     "union": false,
                     "idlType": {
+                        "type": "dictionary-type",
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -78,6 +83,7 @@
                 "name": "reqSeq",
                 "required": true,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -100,6 +106,7 @@
                 "name": "h",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -113,6 +120,7 @@
                 "name": "d",
                 "required": false,
                 "idlType": {
+                    "type": "dictionary-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -124,4 +132,4 @@
         ],
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/documentation-dos.json b/test/syntax/json/documentation-dos.json
index 340e039b4495d7..baa0b5a09b5ee1 100644
--- a/test/syntax/json/documentation-dos.json
+++ b/test/syntax/json/documentation-dos.json
@@ -7,4 +7,4 @@
         "inheritance": null,
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/documentation.json b/test/syntax/json/documentation.json
index 340e039b4495d7..baa0b5a09b5ee1 100644
--- a/test/syntax/json/documentation.json
+++ b/test/syntax/json/documentation.json
@@ -7,4 +7,4 @@
         "inheritance": null,
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/enum.json b/test/syntax/json/enum.json
index 88a608ba632232..29d1c865b68eab 100644
--- a/test/syntax/json/enum.json
+++ b/test/syntax/json/enum.json
@@ -3,9 +3,18 @@
         "type": "enum",
         "name": "MealType",
         "values": [
-            { "type": "string", "value": "rice" },
-            { "type": "string", "value": "noodles" },
-            { "type": "string", "value": "other" }
+            {
+                "type": "string",
+                "value": "rice"
+            },
+            {
+                "type": "string",
+                "value": "noodles"
+            },
+            {
+                "type": "string",
+                "value": "other"
+            }
         ],
         "extAttrs": []
     },
@@ -21,6 +30,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -37,6 +47,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -54,6 +65,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -67,6 +79,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -80,6 +93,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -99,9 +113,18 @@
         "type": "enum",
         "name": "AltMealType",
         "values": [
-            { "type": "string", "value": "rice" },
-            { "type": "string", "value": "noodles" },
-            { "type": "string", "value": "other" }
+            {
+                "type": "string",
+                "value": "rice"
+            },
+            {
+                "type": "string",
+                "value": "noodles"
+            },
+            {
+                "type": "string",
+                "value": "other"
+            }
         ],
         "extAttrs": []
     }
diff --git a/test/syntax/json/equivalent-decl.json b/test/syntax/json/equivalent-decl.json
index 7ef08bc595ffcf..de8d4dbc70ba8d 100644
--- a/test/syntax/json/equivalent-decl.json
+++ b/test/syntax/json/equivalent-decl.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -28,6 +29,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -41,6 +43,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -60,6 +63,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -73,6 +77,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -86,6 +91,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -113,6 +119,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -130,6 +137,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -143,6 +151,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -162,6 +171,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -175,6 +185,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -188,6 +199,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -207,6 +219,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -220,6 +233,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -239,6 +253,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -252,6 +267,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -265,6 +281,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/extended-attributes.json b/test/syntax/json/extended-attributes.json
index 6526e2a35997af..e0dc2360f3af08 100644
--- a/test/syntax/json/extended-attributes.json
+++ b/test/syntax/json/extended-attributes.json
@@ -30,139 +30,205 @@
         ]
     },
     {
-      "type": "interface",
-      "name": "IdInterface",
-      "partial": false,
-      "members": [],
-      "inheritance": null,
-      "extAttrs": [
-        {
-          "name": "IntAttr",
-          "arguments": null,
-          "type": "extended-attribute",
-          "rhs": {
-            "type": "integer",
-            "value": "0"
-          }
-        },
-        {
-          "name": "FloatAttr",
-          "arguments": null,
-          "type": "extended-attribute",
-          "rhs": {
-            "type": "float",
-            "value": "3.14"
-          }
-        },
-        {
-          "name": "StringAttr",
-          "arguments": null,
-          "type": "extended-attribute",
-          "rhs": {
-            "type": "string",
-            "value": "\"abc\""
-          }
-        }
-      ]
+        "type": "interface",
+        "name": "IdInterface",
+        "partial": false,
+        "members": [],
+        "inheritance": null,
+        "extAttrs": [
+            {
+                "name": "IntAttr",
+                "arguments": null,
+                "type": "extended-attribute",
+                "rhs": {
+                    "type": "integer",
+                    "value": "0"
+                }
+            },
+            {
+                "name": "FloatAttr",
+                "arguments": null,
+                "type": "extended-attribute",
+                "rhs": {
+                    "type": "float",
+                    "value": "3.14"
+                }
+            },
+            {
+                "name": "StringAttr",
+                "arguments": null,
+                "type": "extended-attribute",
+                "rhs": {
+                    "type": "string",
+                    "value": "\"abc\""
+                }
+            }
+        ]
     },
     {
-      "type": "interface",
-      "name": "Circle",
-      "partial": false,
-      "members": [
-        {
-          "type": "attribute",
-          "static": false,
-          "stringifier": false,
-          "inherit": false,
-          "readonly": false,
-          "idlType": {
-            "sequence": false,
-            "generic": null,
-            "nullable": false,
-            "union": false,
-            "idlType": "double"
-          },
-          "name": "r",
-          "extAttrs": []
-        },
-        {
-          "type": "attribute",
-          "static": false,
-          "stringifier": false,
-          "inherit": false,
-          "readonly": false,
-          "idlType": {
-            "sequence": false,
-            "generic": null,
-            "nullable": false,
-            "union": false,
-            "idlType": "double"
-          },
-          "name": "cx",
-          "extAttrs": []
-        },
-        {
-          "type": "attribute",
-          "static": false,
-          "stringifier": false,
-          "inherit": false,
-          "readonly": false,
-          "idlType": {
-            "sequence": false,
-            "generic": null,
-            "nullable": false,
-            "union": false,
-            "idlType": "double"
-          },
-          "name": "cy",
-          "extAttrs": []
-        },
-        {
-          "type": "attribute",
-          "static": false,
-          "stringifier": false,
-          "inherit": false,
-          "readonly": true,
-          "idlType": {
-            "sequence": false,
-            "generic": null,
-            "nullable": false,
-            "union": false,
-            "idlType": "double"
-          },
-          "name": "circumference",
-          "extAttrs": []
-        }
-      ],
-      "inheritance": null,
-      "extAttrs": [
-        {
-          "name": "Constructor",
-          "arguments": null,
-          "type": "extended-attribute",
-          "rhs": null
-        },
-        {
-          "name": "Constructor",
-          "arguments": [
+        "type": "interface",
+        "name": "Circle",
+        "partial": false,
+        "members": [
+            {
+                "type": "attribute",
+                "static": false,
+                "stringifier": false,
+                "inherit": false,
+                "readonly": false,
+                "idlType": {
+                    "type": "attribute-type",
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "double"
+                },
+                "name": "r",
+                "extAttrs": []
+            },
+            {
+                "type": "attribute",
+                "static": false,
+                "stringifier": false,
+                "inherit": false,
+                "readonly": false,
+                "idlType": {
+                    "type": "attribute-type",
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "double"
+                },
+                "name": "cx",
+                "extAttrs": []
+            },
             {
-              "optional": false,
-              "variadic": false,
-              "extAttrs": [],
-              "idlType": {
-                "sequence": false,
-                "generic": null,
-                "nullable": false,
-                "union": false,
-                "idlType": "double"
-              },
-              "name": "radius"
+                "type": "attribute",
+                "static": false,
+                "stringifier": false,
+                "inherit": false,
+                "readonly": false,
+                "idlType": {
+                    "type": "attribute-type",
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "double"
+                },
+                "name": "cy",
+                "extAttrs": []
+            },
+            {
+                "type": "attribute",
+                "static": false,
+                "stringifier": false,
+                "inherit": false,
+                "readonly": true,
+                "idlType": {
+                    "type": "attribute-type",
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "double"
+                },
+                "name": "circumference",
+                "extAttrs": []
+            }
+        ],
+        "inheritance": null,
+        "extAttrs": [
+            {
+                "name": "Constructor",
+                "arguments": null,
+                "type": "extended-attribute",
+                "rhs": null
+            },
+            {
+                "name": "Constructor",
+                "arguments": [
+                    {
+                        "optional": false,
+                        "variadic": false,
+                        "extAttrs": [],
+                        "idlType": {
+                            "type": "argument-type",
+                            "sequence": false,
+                            "generic": null,
+                            "nullable": false,
+                            "union": false,
+                            "idlType": "double"
+                        },
+                        "name": "radius"
+                    }
+                ],
+                "type": "extended-attribute",
+                "rhs": null
+            }
+        ]
+    },
+    {
+        "type": "interface",
+        "name": "I",
+        "partial": false,
+        "members": [
+            {
+                "type": "attribute",
+                "static": false,
+                "stringifier": false,
+                "inherit": false,
+                "readonly": false,
+                "idlType": {
+                    "type": "attribute-type",
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": true,
+                    "idlType": [
+                        {
+                            "type": null,
+                            "sequence": false,
+                            "generic": null,
+                            "nullable": false,
+                            "union": false,
+                            "idlType": "long"
+                        },
+                        {
+                            "type": null,
+                            "sequence": false,
+                            "generic": null,
+                            "nullable": false,
+                            "union": false,
+                            "idlType": "Node"
+                        }
+                    ],
+                    "extAttrs": [
+                        {
+                            "name": "XAttr",
+                            "arguments": null,
+                            "type": "extended-attribute",
+                            "rhs": null
+                        }
+                    ]
+                },
+                "name": "attrib",
+                "extAttrs": []
+            }
+        ],
+        "inheritance": null,
+        "extAttrs": [
+            {
+                "name": "Exposed",
+                "arguments": null,
+                "type": "extended-attribute",
+                "rhs": {
+                    "type": "identifier",
+                    "value": "Window"
+                }
             }
-          ],
-          "type": "extended-attribute",
-          "rhs": null
-        }
-      ]
+        ]
     }
 ]
diff --git a/test/syntax/json/generic.json b/test/syntax/json/generic.json
index 214ddd8e994872..62593859fb14ce 100644
--- a/test/syntax/json/generic.json
+++ b/test/syntax/json/generic.json
@@ -12,21 +12,25 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": "Promise",
                     "nullable": false,
                     "union": false,
                     "idlType": {
+                        "type": "return-type",
                         "sequence": false,
                         "generic": "ResponsePromise",
                         "nullable": false,
                         "union": false,
                         "idlType": {
+                            "type": "return-type",
                             "sequence": true,
                             "generic": "sequence",
                             "nullable": false,
                             "union": false,
                             "idlType": {
+                                "type": "return-type",
                                 "sequence": false,
                                 "generic": null,
                                 "nullable": true,
@@ -47,11 +51,13 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": "Promise",
                     "nullable": false,
                     "union": false,
                     "idlType": {
+                        "type": "attribute-type",
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -79,11 +85,13 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": "Promise",
                     "nullable": false,
                     "union": false,
                     "idlType": {
+                        "type": "return-type",
                         "sequence": false,
                         "generic": null,
                         "nullable": true,
@@ -103,11 +111,13 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": "Promise",
                     "nullable": false,
                     "union": false,
                     "idlType": {
+                        "type": "return-type",
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -136,11 +146,13 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": "ResponsePromise",
                     "nullable": false,
                     "union": false,
                     "idlType": {
+                        "type": "return-type",
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
diff --git a/test/syntax/json/getter-setter.json b/test/syntax/json/getter-setter.json
index 6268a532d55a24..1213307f20309b 100644
--- a/test/syntax/json/getter-setter.json
+++ b/test/syntax/json/getter-setter.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -28,6 +29,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -41,6 +43,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -60,6 +63,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -73,6 +77,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -86,6 +91,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/identifier-qualified-names.json b/test/syntax/json/identifier-qualified-names.json
index 11568f8cfd8cc3..f4e295acd3e120 100644
--- a/test/syntax/json/identifier-qualified-names.json
+++ b/test/syntax/json/identifier-qualified-names.json
@@ -2,6 +2,7 @@
     {
         "type": "typedef",
         "idlType": {
+            "type": "typedef-type",
             "sequence": false,
             "generic": null,
             "nullable": false,
@@ -24,6 +25,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -37,6 +39,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -56,6 +59,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -69,6 +73,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -96,6 +101,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -112,6 +118,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": true,
@@ -138,6 +145,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -151,6 +159,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/implements.json b/test/syntax/json/implements.json
index fba0542780818c..69879d94f553d5 100644
--- a/test/syntax/json/implements.json
+++ b/test/syntax/json/implements.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -37,6 +38,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -50,6 +52,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -63,6 +66,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -76,6 +80,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/indexed-properties.json b/test/syntax/json/indexed-properties.json
index 2676c0efab34a6..697b595546c788 100644
--- a/test/syntax/json/indexed-properties.json
+++ b/test/syntax/json/indexed-properties.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -28,6 +29,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -41,6 +43,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -60,6 +63,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -73,6 +77,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -86,6 +91,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -105,6 +111,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -118,6 +125,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -137,6 +145,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -150,6 +159,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -169,6 +179,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -182,6 +193,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -195,6 +207,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -214,6 +227,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -227,6 +241,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/inherits-getter.json b/test/syntax/json/inherits-getter.json
index ba6bafdf3913c9..818d8b6c16f824 100644
--- a/test/syntax/json/inherits-getter.json
+++ b/test/syntax/json/inherits-getter.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -36,6 +37,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -52,6 +54,7 @@
                 "inherit": true,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -65,4 +68,4 @@
         "inheritance": "Animal",
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/interface-inherits.json b/test/syntax/json/interface-inherits.json
index e78c1cce865e4d..74a4c39bb0ffb1 100644
--- a/test/syntax/json/interface-inherits.json
+++ b/test/syntax/json/interface-inherits.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -36,6 +37,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -61,6 +63,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -74,4 +77,4 @@
         "inheritance": "Animal",
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/iterable.json b/test/syntax/json/iterable.json
index 1e92307dad53ae..7126a4ea2b01b1 100644
--- a/test/syntax/json/iterable.json
+++ b/test/syntax/json/iterable.json
@@ -6,13 +6,16 @@
         "members": [
             {
                 "type": "iterable",
-                "idlType": {
-                    "sequence": false,
-                    "generic": null,
-                    "nullable": false,
-                    "union": false,
-                    "idlType": "long"
-                },
+                "idlType": [
+                    {
+                        "type": null,
+                        "sequence": false,
+                        "generic": null,
+                        "nullable": false,
+                        "union": false,
+                        "idlType": "long"
+                    }
+                ],
                 "extAttrs": []
             }
         ],
@@ -28,6 +31,7 @@
                 "type": "iterable",
                 "idlType": [
                     {
+                        "type": null,
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -35,6 +39,7 @@
                         "idlType": "short"
                     },
                     {
+                        "type": null,
                         "sequence": false,
                         "generic": null,
                         "nullable": true,
@@ -55,21 +60,24 @@
         "members": [
             {
                 "type": "iterable",
-                "idlType": {
-                    "sequence": false,
-                    "generic": null,
-                    "nullable": false,
-                    "union": false,
-                    "idlType": "long",
-                    "extAttrs": [
-                        {
-                            "name": "XAttr",
-                            "arguments": null,
-                            "type": "extended-attribute",
-                            "rhs": null
-                        }
-                    ]
-                },
+                "idlType": [
+                    {
+                        "type": null,
+                        "sequence": false,
+                        "generic": null,
+                        "nullable": false,
+                        "union": false,
+                        "idlType": "long",
+                        "extAttrs": [
+                            {
+                                "name": "XAttr",
+                                "arguments": null,
+                                "type": "extended-attribute",
+                                "rhs": null
+                            }
+                        ]
+                    }
+                ],
                 "extAttrs": []
             }
         ],
@@ -77,4 +85,3 @@
         "extAttrs": []
     }
 ]
-
diff --git a/test/syntax/json/legacyiterable.json b/test/syntax/json/legacyiterable.json
index 059ccc11312fc6..5a1e526b50ae60 100644
--- a/test/syntax/json/legacyiterable.json
+++ b/test/syntax/json/legacyiterable.json
@@ -6,13 +6,16 @@
         "members": [
             {
                 "type": "legacyiterable",
-                "idlType": {
-                    "sequence": false,
-                    "generic": null,
-                    "nullable": false,
-                    "union": false,
-                    "idlType": "long"
-                },
+                "idlType": [
+                    {
+                        "type": null,
+                        "sequence": false,
+                        "generic": null,
+                        "nullable": false,
+                        "union": false,
+                        "idlType": "long"
+                    }
+                ],
                 "extAttrs": []
             }
         ],
@@ -20,4 +23,3 @@
         "extAttrs": []
     }
 ]
-
diff --git a/test/syntax/json/maplike.json b/test/syntax/json/maplike.json
index 97e76d5841a24c..b86e10487c1b61 100644
--- a/test/syntax/json/maplike.json
+++ b/test/syntax/json/maplike.json
@@ -8,6 +8,7 @@
                 "type": "maplike",
                 "idlType": [
                     {
+                        "type": null,
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -15,6 +16,7 @@
                         "idlType": "long"
                     },
                     {
+                        "type": null,
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -38,6 +40,7 @@
                 "type": "maplike",
                 "idlType": [
                     {
+                        "type": null,
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -45,6 +48,7 @@
                         "idlType": "long"
                     },
                     {
+                        "type": null,
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -68,6 +72,7 @@
                 "type": "maplike",
                 "idlType": [
                     {
+                        "type": null,
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -83,6 +88,7 @@
                         ]
                     },
                     {
+                        "type": null,
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -106,4 +112,3 @@
         "extAttrs": []
     }
 ]
-
diff --git a/test/syntax/json/mixin.json b/test/syntax/json/mixin.json
index a2afae318dcc13..f0458e2b0841ca 100644
--- a/test/syntax/json/mixin.json
+++ b/test/syntax/json/mixin.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -47,6 +48,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
diff --git a/test/syntax/json/namedconstructor.json b/test/syntax/json/namedconstructor.json
index cee163069d1850..f895461d15e0a5 100644
--- a/test/syntax/json/namedconstructor.json
+++ b/test/syntax/json/namedconstructor.json
@@ -23,6 +23,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -40,4 +41,4 @@
             }
         ]
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/namespace.json b/test/syntax/json/namespace.json
index 8ee7796553ed9e..0611b710bf10d9 100644
--- a/test/syntax/json/namespace.json
+++ b/test/syntax/json/namespace.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -28,6 +29,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -41,6 +43,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -54,6 +57,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -73,6 +77,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -86,6 +91,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -99,6 +105,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/nointerfaceobject.json b/test/syntax/json/nointerfaceobject.json
index 85987e82de3db4..03bb99442d5fe3 100644
--- a/test/syntax/json/nointerfaceobject.json
+++ b/test/syntax/json/nointerfaceobject.json
@@ -12,6 +12,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -25,6 +26,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/nullable.json b/test/syntax/json/nullable.json
index 2c83c3dad58c67..ae4d2aa537594c 100644
--- a/test/syntax/json/nullable.json
+++ b/test/syntax/json/nullable.json
@@ -7,7 +7,10 @@
             {
                 "type": "const",
                 "nullable": true,
-                "idlType": "boolean",
+                "idlType": {
+                    "type": "const-type",
+                    "idlType": "boolean"
+                },
                 "name": "ARE_WE_THERE_YET",
                 "value": {
                     "type": "boolean",
@@ -31,6 +34,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": true,
@@ -44,4 +48,4 @@
         "inheritance": null,
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/nullableobjects.json b/test/syntax/json/nullableobjects.json
index 2c875607262007..29d1314f168651 100644
--- a/test/syntax/json/nullableobjects.json
+++ b/test/syntax/json/nullableobjects.json
@@ -28,6 +28,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -41,6 +42,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": true,
@@ -60,6 +62,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -73,6 +76,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": true,
diff --git a/test/syntax/json/operation-optional-arg.json b/test/syntax/json/operation-optional-arg.json
index 7588d63475f8f6..44c3a16dc2ee1a 100644
--- a/test/syntax/json/operation-optional-arg.json
+++ b/test/syntax/json/operation-optional-arg.json
@@ -12,6 +12,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -25,6 +26,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -38,6 +40,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -51,6 +54,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -64,6 +68,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/overloading.json b/test/syntax/json/overloading.json
index 8d7e8e286cbfdc..87169e9202ba40 100644
--- a/test/syntax/json/overloading.json
+++ b/test/syntax/json/overloading.json
@@ -28,6 +28,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -41,6 +42,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -60,6 +62,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -73,6 +76,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -101,6 +105,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -114,6 +119,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -133,6 +139,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -153,6 +160,7 @@
                             }
                         ],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -166,6 +174,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -179,6 +188,7 @@
                         "variadic": true,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -198,6 +208,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -216,6 +227,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -229,6 +241,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -242,6 +255,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -255,6 +269,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -268,6 +283,7 @@
                         "variadic": true,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/overridebuiltins.json b/test/syntax/json/overridebuiltins.json
index 4ded17c3103772..d63f8f744113ee 100644
--- a/test/syntax/json/overridebuiltins.json
+++ b/test/syntax/json/overridebuiltins.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -28,6 +29,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -41,6 +43,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/partial-interface.json b/test/syntax/json/partial-interface.json
index e95af2baa1548b..c16c64d334dfc4 100644
--- a/test/syntax/json/partial-interface.json
+++ b/test/syntax/json/partial-interface.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -36,6 +37,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -48,4 +50,4 @@
         ],
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/primitives.json b/test/syntax/json/primitives.json
index 7568542f95762f..cf965399a4ff3e 100644
--- a/test/syntax/json/primitives.json
+++ b/test/syntax/json/primitives.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -27,6 +28,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -43,6 +45,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -59,6 +62,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -75,6 +79,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -91,6 +96,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -107,6 +113,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -123,6 +130,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -139,6 +147,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -155,6 +164,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -171,6 +181,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -187,6 +198,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -203,6 +215,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -219,6 +232,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -235,6 +249,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -251,6 +266,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -267,6 +283,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -280,4 +297,4 @@
         "inheritance": null,
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/prototyperoot.json b/test/syntax/json/prototyperoot.json
index c75f00ed3e84f2..eda7f14dae4c5d 100644
--- a/test/syntax/json/prototyperoot.json
+++ b/test/syntax/json/prototyperoot.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
diff --git a/test/syntax/json/putforwards.json b/test/syntax/json/putforwards.json
index 1b0a7b6b9743f0..4b809d2d34dcb5 100644
--- a/test/syntax/json/putforwards.json
+++ b/test/syntax/json/putforwards.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -37,6 +38,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -50,4 +52,4 @@
         "inheritance": null,
         "extAttrs": []
     }
-]
\ No newline at end of file
+]
diff --git a/test/syntax/json/record.json b/test/syntax/json/record.json
index 339ae08a39f38b..dd00b5df045e5c 100644
--- a/test/syntax/json/record.json
+++ b/test/syntax/json/record.json
@@ -12,6 +12,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -25,17 +26,20 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": true,
                             "generic": "sequence",
                             "nullable": false,
                             "union": false,
                             "idlType": {
+                                "type": "argument-type",
                                 "sequence": false,
                                 "generic": "record",
                                 "nullable": false,
                                 "union": false,
                                 "idlType": [
                                     {
+                                        "type": "argument-type",
                                         "sequence": false,
                                         "generic": null,
                                         "nullable": false,
@@ -43,6 +47,7 @@
                                         "idlType": "ByteString"
                                     },
                                     {
+                                        "type": "argument-type",
                                         "sequence": false,
                                         "generic": null,
                                         "nullable": false,
@@ -65,12 +70,14 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": "record",
                     "nullable": false,
                     "union": false,
                     "idlType": [
                         {
+                            "type": "return-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -78,12 +85,14 @@
                             "idlType": "DOMString"
                         },
                         {
+                            "type": "return-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": true,
                             "union": true,
                             "idlType": [
                                 {
+                                    "type": null,
                                     "sequence": false,
                                     "generic": null,
                                     "nullable": false,
@@ -91,6 +100,7 @@
                                     "idlType": "float"
                                 },
                                 {
+                                    "type": null,
                                     "sequence": false,
                                     "generic": null,
                                     "nullable": false,
@@ -113,6 +123,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -134,12 +145,14 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": "record",
                             "nullable": false,
                             "union": false,
                             "idlType": [
                                 {
+                                    "type": "argument-type",
                                     "sequence": false,
                                     "generic": null,
                                     "nullable": false,
@@ -147,6 +160,7 @@
                                     "idlType": "USVString"
                                 },
                                 {
+                                    "type": "argument-type",
                                     "sequence": false,
                                     "generic": null,
                                     "nullable": false,
@@ -176,12 +190,14 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": "record",
                     "nullable": false,
                     "union": false,
                     "idlType": [
                         {
+                            "type": "return-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -189,6 +205,7 @@
                             "idlType": "DOMString"
                         },
                         {
+                            "type": "return-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/reg-operations.json b/test/syntax/json/reg-operations.json
index c1c13c74f1baac..d696e907e0c663 100644
--- a/test/syntax/json/reg-operations.json
+++ b/test/syntax/json/reg-operations.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -27,6 +28,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -53,6 +55,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -71,6 +74,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -84,6 +88,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -103,6 +108,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -116,6 +122,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -129,6 +136,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/replaceable.json b/test/syntax/json/replaceable.json
index f53009b4baa42b..a10b0bfd03b022 100644
--- a/test/syntax/json/replaceable.json
+++ b/test/syntax/json/replaceable.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -35,6 +36,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
diff --git a/test/syntax/json/sequence.json b/test/syntax/json/sequence.json
index 79821181a19a52..c2d1765bfa506d 100644
--- a/test/syntax/json/sequence.json
+++ b/test/syntax/json/sequence.json
@@ -12,6 +12,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -25,11 +26,13 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": true,
                             "generic": "sequence",
                             "nullable": false,
                             "union": false,
                             "idlType": {
+                                "type": "argument-type",
                                 "sequence": false,
                                 "generic": null,
                                 "nullable": false,
@@ -50,11 +53,13 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": true,
                     "generic": "sequence",
                     "nullable": false,
                     "union": false,
                     "idlType": {
+                        "type": "return-type",
                         "sequence": false,
                         "generic": null,
                         "nullable": false,
@@ -75,7 +80,6 @@
         "name": "Foo",
         "partial": false,
         "members": [
-
             {
                 "type": "operation",
                 "getter": false,
@@ -84,6 +88,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -98,7 +103,6 @@
         "inheritance": null,
         "extAttrs": []
     },
-
     {
         "type": "interface",
         "name": "I",
@@ -112,6 +116,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -125,11 +130,13 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": true,
                             "generic": "sequence",
                             "nullable": false,
                             "union": false,
                             "idlType": {
+                                "type": "argument-type",
                                 "sequence": false,
                                 "generic": null,
                                 "nullable": false,
diff --git a/test/syntax/json/setlike.json b/test/syntax/json/setlike.json
index 3c1591b2372256..12299a7ee0444a 100644
--- a/test/syntax/json/setlike.json
+++ b/test/syntax/json/setlike.json
@@ -6,13 +6,16 @@
         "members": [
             {
                 "type": "setlike",
-                "idlType": {
-                    "sequence": false,
-                    "generic": null,
-                    "nullable": false,
-                    "union": false,
-                    "idlType": "long"
-                },
+                "idlType": [
+                    {
+                        "type": null,
+                        "sequence": false,
+                        "generic": null,
+                        "nullable": false,
+                        "union": false,
+                        "idlType": "long"
+                    }
+                ],
                 "readonly": false,
                 "extAttrs": []
             }
@@ -27,13 +30,16 @@
         "members": [
             {
                 "type": "setlike",
-                "idlType": {
-                    "sequence": false,
-                    "generic": null,
-                    "nullable": false,
-                    "union": false,
-                    "idlType": "long"
-                },
+                "idlType": [
+                    {
+                        "type": null,
+                        "sequence": false,
+                        "generic": null,
+                        "nullable": false,
+                        "union": false,
+                        "idlType": "long"
+                    }
+                ],
                 "readonly": true,
                 "extAttrs": []
             }
@@ -48,21 +54,24 @@
         "members": [
             {
                 "type": "setlike",
-                "idlType": {
-                    "sequence": false,
-                    "generic": null,
-                    "nullable": false,
-                    "union": false,
-                    "idlType": "long",
-                    "extAttrs": [
-                        {
-                            "name": "XAttr",
-                            "arguments": null,
-                            "type": "extended-attribute",
-                            "rhs": null
-                        }
-                    ]
-                },
+                "idlType": [
+                    {
+                        "type": null,
+                        "sequence": false,
+                        "generic": null,
+                        "nullable": false,
+                        "union": false,
+                        "idlType": "long",
+                        "extAttrs": [
+                            {
+                                "name": "XAttr",
+                                "arguments": null,
+                                "type": "extended-attribute",
+                                "rhs": null
+                            }
+                        ]
+                    }
+                ],
                 "readonly": false,
                 "extAttrs": []
             }
@@ -71,4 +80,3 @@
         "extAttrs": []
     }
 ]
-
diff --git a/test/syntax/json/static.json b/test/syntax/json/static.json
index 034ffda2d5450c..0951b2acf5ff99 100644
--- a/test/syntax/json/static.json
+++ b/test/syntax/json/static.json
@@ -19,6 +19,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -35,6 +36,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -51,6 +53,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -67,6 +70,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -84,6 +88,7 @@
                 "static": true,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -97,6 +102,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -110,6 +116,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -123,6 +130,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/stringifier-attribute.json b/test/syntax/json/stringifier-attribute.json
index acb26c2dda8879..36e2b6d50ac064 100644
--- a/test/syntax/json/stringifier-attribute.json
+++ b/test/syntax/json/stringifier-attribute.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -27,6 +28,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
diff --git a/test/syntax/json/stringifier-custom.json b/test/syntax/json/stringifier-custom.json
index 3c84305d863847..3dc3ac1758c8a2 100644
--- a/test/syntax/json/stringifier-custom.json
+++ b/test/syntax/json/stringifier-custom.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -27,6 +28,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": true,
@@ -43,6 +45,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -60,6 +63,7 @@
                 "static": false,
                 "stringifier": true,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
diff --git a/test/syntax/json/stringifier.json b/test/syntax/json/stringifier.json
index 6b2d133d96f185..1a702765b0a656 100644
--- a/test/syntax/json/stringifier.json
+++ b/test/syntax/json/stringifier.json
@@ -12,6 +12,7 @@
                 "static": false,
                 "stringifier": true,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
diff --git a/test/syntax/json/treatasnull.json b/test/syntax/json/treatasnull.json
index 03dec604fb44f6..611d9741043947 100644
--- a/test/syntax/json/treatasnull.json
+++ b/test/syntax/json/treatasnull.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -27,6 +28,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -44,6 +46,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -67,6 +70,7 @@
                             }
                         ],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/treatasundefined.json b/test/syntax/json/treatasundefined.json
index 8699b73c8f2db2..258acdabd8593d 100644
--- a/test/syntax/json/treatasundefined.json
+++ b/test/syntax/json/treatasundefined.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -27,6 +28,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -44,6 +46,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -67,6 +70,7 @@
                             }
                         ],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/syntax/json/typedef-union.json b/test/syntax/json/typedef-union.json
index 9c87672c8aebb1..06735a80791006 100644
--- a/test/syntax/json/typedef-union.json
+++ b/test/syntax/json/typedef-union.json
@@ -1,49 +1,48 @@
 [
-   {
-      "type" : "typedef",
-      "idlType" : {
-         "nullable" : false,
-         "generic" : null,
-         "union" : true,
-         "idlType" : [
-            {
-               "union" : false,
-               "generic" : null,
-               "nullable" : false,
-               "array" : false,
-               "sequence" : false,
-               "idlType" : "ImageData"
-            },
-            {
-               "generic" : null,
-               "union" : false,
-               "nullable" : false,
-               "array" : false,
-               "idlType" : "HTMLImageElement",
-               "sequence" : false
-            },
-            {
-               "array" : false,
-               "sequence" : false,
-               "idlType" : "HTMLCanvasElement",
-               "generic" : null,
-               "union" : false,
-               "nullable" : false
-            },
-            {
-               "union" : false,
-               "generic" : null,
-               "nullable" : false,
-               "array" : false,
-               "sequence" : false,
-               "idlType" : "HTMLVideoElement"
-            }
-         ],
-         "sequence" : false,
-         "array" : false
-      },
-      "name" : "TexImageSource",
-      "extAttrs" : [],
-      "typeExtAttrs" : []
-   }
+    {
+        "type": "typedef",
+        "idlType": {
+            "type": "typedef-type",
+            "sequence": false,
+            "generic": null,
+            "nullable": false,
+            "union": true,
+            "idlType": [
+                {
+                    "type": null,
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "ImageData"
+                },
+                {
+                    "type": null,
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "HTMLImageElement"
+                },
+                {
+                    "type": null,
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "HTMLCanvasElement"
+                },
+                {
+                    "type": null,
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": false,
+                    "idlType": "HTMLVideoElement"
+                }
+            ]
+        },
+        "name": "TexImageSource",
+        "extAttrs": []
+    }
 ]
diff --git a/test/syntax/json/typedef.json b/test/syntax/json/typedef.json
index 612cfe727d91aa..5e9715da8fb2a7 100644
--- a/test/syntax/json/typedef.json
+++ b/test/syntax/json/typedef.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -27,6 +28,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -43,11 +45,13 @@
     {
         "type": "typedef",
         "idlType": {
+            "type": "typedef-type",
             "sequence": true,
             "generic": "sequence",
             "nullable": false,
             "union": false,
             "idlType": {
+                "type": "typedef-type",
                 "sequence": false,
                 "generic": null,
                 "nullable": false,
@@ -70,6 +74,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -86,6 +91,7 @@
                 "inherit": false,
                 "readonly": false,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -111,6 +117,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -128,6 +135,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -141,6 +149,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -160,6 +169,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -173,6 +183,7 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -191,6 +202,7 @@
     {
         "type": "typedef",
         "idlType": {
+            "type": "typedef-type",
             "sequence": false,
             "generic": null,
             "nullable": false,
diff --git a/test/syntax/json/typesuffixes.json b/test/syntax/json/typesuffixes.json
index 0b30830a158db8..be0b1f226827d0 100644
--- a/test/syntax/json/typesuffixes.json
+++ b/test/syntax/json/typesuffixes.json
@@ -12,6 +12,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -25,11 +26,13 @@
                         "variadic": false,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": true,
                             "generic": "sequence",
                             "nullable": true,
                             "union": false,
                             "idlType": {
+                                "type": "argument-type",
                                 "sequence": false,
                                 "generic": null,
                                 "nullable": true,
diff --git a/test/syntax/json/uniontype.json b/test/syntax/json/uniontype.json
index c4725d417b5378..87735c7fb6320d 100644
--- a/test/syntax/json/uniontype.json
+++ b/test/syntax/json/uniontype.json
@@ -1,118 +1,129 @@
 [
-   {
-      "partial": false,
-      "members": [
-         {
-            "idlType": {
-               "idlType": [
-                  {
-                     "union": false,
-                     "sequence": false,
-                     "generic": null,
-                     "idlType": "float",
-                     "nullable": false
-                  },
-                  {
-                     "idlType": [
+    {
+        "type": "interface",
+        "name": "Union",
+        "partial": false,
+        "members": [
+            {
+                "type": "attribute",
+                "static": false,
+                "stringifier": false,
+                "inherit": false,
+                "readonly": false,
+                "idlType": {
+                    "type": "attribute-type",
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": true,
+                    "idlType": [
                         {
-                           "nullable": false,
-                           "idlType": "Date",
-                           "sequence": false,
-                           "generic": null,
-                           "union": false
+                            "type": null,
+                            "sequence": false,
+                            "generic": null,
+                            "nullable": false,
+                            "union": false,
+                            "idlType": "float"
                         },
                         {
-                           "nullable": false,
-                           "idlType": "Event",
-                           "generic": null,
-                           "sequence": false,
-                           "union": false
-                        }
-                     ],
-                     "nullable": false,
-                     "sequence": false,
-                     "generic": null,
-                     "union": true
-                  },
-                  {
-                     "generic": null,
-                     "sequence": false,
-                     "idlType": [
-                        {
-                           "union": false,
-                           "sequence": false,
-                           "generic": null,
-                           "nullable": false,
-                           "idlType": "Node"
+                            "type": null,
+                            "sequence": false,
+                            "generic": null,
+                            "nullable": false,
+                            "union": true,
+                            "idlType": [
+                                {
+                                    "type": null,
+                                    "sequence": false,
+                                    "generic": null,
+                                    "nullable": false,
+                                    "union": false,
+                                    "idlType": "Date"
+                                },
+                                {
+                                    "type": null,
+                                    "sequence": false,
+                                    "generic": null,
+                                    "nullable": false,
+                                    "union": false,
+                                    "idlType": "Event"
+                                }
+                            ]
                         },
                         {
-                           "nullable": false,
-                           "idlType": "DOMString",
-                           "sequence": false,
-                           "generic": null,
-                           "union": false
+                            "type": null,
+                            "sequence": false,
+                            "generic": null,
+                            "nullable": true,
+                            "union": true,
+                            "idlType": [
+                                {
+                                    "type": null,
+                                    "sequence": false,
+                                    "generic": null,
+                                    "nullable": false,
+                                    "union": false,
+                                    "idlType": "Node"
+                                },
+                                {
+                                    "type": null,
+                                    "sequence": false,
+                                    "generic": null,
+                                    "nullable": false,
+                                    "union": false,
+                                    "idlType": "DOMString"
+                                }
+                            ]
                         }
-                     ],
-                     "nullable": true,
-                     "union": true
-                  }
-               ],
-               "nullable": false,
-               "generic": null,
-               "sequence": false,
-               "union": true
+                    ]
+                },
+                "name": "test",
+                "extAttrs": []
             },
-            "name": "test",
-            "inherit": false,
-            "type": "attribute",
-            "extAttrs": [],
-            "readonly": false,
-            "stringifier": false,
-            "static": false
-         },
-         {
-            "readonly": false,
-            "extAttrs": [],
-            "stringifier": false,
-            "static": false,
-            "name": "test2",
-            "idlType": {
-               "nullable": false,
-               "idlType": [
-                  {
-                     "extAttrs": [
+            {
+                "type": "attribute",
+                "static": false,
+                "stringifier": false,
+                "inherit": false,
+                "readonly": false,
+                "idlType": {
+                    "type": "attribute-type",
+                    "sequence": false,
+                    "generic": null,
+                    "nullable": false,
+                    "union": true,
+                    "idlType": [
                         {
-                           "name": "EnforceRange",
-                           "arguments": null,
-                           "type": "extended-attribute",
-                           "rhs": null
+                            "type": null,
+                            "sequence": false,
+                            "generic": null,
+                            "nullable": false,
+                            "union": false,
+                            "idlType": "long",
+                            "extAttrs": [
+                                {
+                                    "name": "EnforceRange",
+                                    "arguments": null,
+                                    "type": "extended-attribute",
+                                    "rhs": null
+                                }
+                            ]
+                        },
+                        {
+                            "type": null,
+                            "sequence": false,
+                            "generic": null,
+                            "nullable": false,
+                            "union": false,
+                            "idlType": "Date"
                         }
-                     ],
-                     "nullable": false,
-                     "idlType": "long",
-                     "generic": null,
-                     "sequence": false,
-                     "union": false
-                  },
-                  {
-                     "union": false,
-                     "sequence": false,
-                     "generic": null,
-                     "idlType": "Date",
-                     "nullable": false
-                  }
-               ],
-               "generic": null,
-               "sequence": false,
-               "union": true
-            },
-            "inherit": false,
-            "type": "attribute"
-         }
-      ],
-      "inheritance": null,
-      "name": "Union",
-      "extAttrs": [],
-      "type": "interface"
-   }
+                    ]
+                },
+                "name": "test2",
+                "extAttrs": []
+            }
+        ],
+        "inheritance": null,
+        "extAttrs": []
+    }
 ]
diff --git a/test/syntax/json/variadic-operations.json b/test/syntax/json/variadic-operations.json
index a9560da9ddd875..53b02dfb4ccb57 100644
--- a/test/syntax/json/variadic-operations.json
+++ b/test/syntax/json/variadic-operations.json
@@ -11,6 +11,7 @@
                 "inherit": false,
                 "readonly": true,
                 "idlType": {
+                    "type": "attribute-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -28,6 +29,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -41,6 +43,7 @@
                         "variadic": true,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
@@ -60,6 +63,7 @@
                 "static": false,
                 "stringifier": false,
                 "idlType": {
+                    "type": "return-type",
                     "sequence": false,
                     "generic": null,
                     "nullable": false,
@@ -73,6 +77,7 @@
                         "variadic": true,
                         "extAttrs": [],
                         "idlType": {
+                            "type": "argument-type",
                             "sequence": false,
                             "generic": null,
                             "nullable": false,
diff --git a/test/util/acquire.js b/test/util/acquire.js
new file mode 100644
index 00000000000000..6f37dd6083c3c7
--- /dev/null
+++ b/test/util/acquire.js
@@ -0,0 +1,8 @@
+"use strict";
+
+const { collect } = require("./collect");
+const fs = require("fs");
+
+for (const test of collect("syntax")) {
+  fs.writeFileSync(test.jsonPath, `${JSON.stringify(test.ast, null, 4)}\n`)
+}
diff --git a/test/util/collect.js b/test/util/collect.js
new file mode 100644
index 00000000000000..7e3d9d3bf31267
--- /dev/null
+++ b/test/util/collect.js
@@ -0,0 +1,59 @@
+"use strict";
+
+const wp = require("../../lib/webidl2");
+const pth = require("path");
+const fs = require("fs");
+const jdp = require("jsondiffpatch");
+
+/**
+ * Collects test items from the specified directory
+ * @param {string} base
+ */
+function* collect(base, { expectError } = {}) {
+  base = pth.join(__dirname, "..", base);
+  const dir = pth.join(base, "idl");
+  const idls = fs.readdirSync(dir)
+    .filter(it => (/\.widl$/).test(it))
+    .map(it => pth.join(dir, it));
+
+  for (const path of idls) {
+    const optFile = pth.join(base, "opt", pth.basename(path)).replace(".widl", ".json");
+    let opt;
+    if (fs.existsSync(optFile))
+      opt = JSON.parse(fs.readFileSync(optFile, "utf8"));
+
+    try {
+      const ast = wp.parse(fs.readFileSync(path, "utf8").replace(/\r\n/g, "\n"), opt);
+      yield new TestItem({ ast, path, opt });
+    }
+    catch (error) {
+      if (expectError) {
+        yield new TestItem({ path, error });
+      }
+      else {
+        throw error;
+      }
+    }
+  }
+};
+
+
+class TestItem {
+  constructor({ ast, path, error, opt }) {
+    this.ast = ast;
+    this.path = path;
+    this.error = error;
+    this.opt = opt;
+    this.jsonPath = pth.join(pth.dirname(path), "../json", pth.basename(path).replace(".widl", ".json"));
+  }
+
+  readJSON() {
+    return JSON.parse(fs.readFileSync(this.jsonPath, "utf8"));
+  }
+
+  diff(target = this.readJSON()) {
+    return jdp.diff(target, this.ast);
+  }
+}
+
+module.exports.collect = collect;
diff --git a/test/writer.js b/test/writer.js
new file mode 100644
index 00000000000000..e84076b4f28ce3
--- /dev/null
+++ b/test/writer.js
@@ -0,0 +1,23 @@
+"use strict";
+
+const { collect } = require("./util/collect");
+const wp = require("../lib/webidl2");
+const writer = require("../lib/writer");
+const expect = require("expect");
+const debug = true;
+
+describe("Rewrite and parses all of the IDLs to produce the same ASTs", () => {
+  for (const test of collect("syntax")) {
+    it(`should produce the same AST for ${test.path}`, () => {
+      try {
+        const diff = test.diff(wp.parse(writer.write(test.ast), test.opt));
+        if (diff && debug) console.log(JSON.stringify(diff, null, 4));
+        expect(diff).toBe(undefined);
+      }
+      catch (e) {
+        console.log(e.toString());
+        throw e;
+      }
+    });
+  }
+});