diff --git a/src/core/inline-idl-parser.js b/src/core/inline-idl-parser.js
index 4eb862c130..0dce75e683 100644
--- a/src/core/inline-idl-parser.js
+++ b/src/core/inline-idl-parser.js
@@ -4,13 +4,14 @@
 
 import { htmlJoinComma, showError } from "./utils.js";
 import { html } from "./import-maps.js";
-const idlPrimitiveRegex = /^[a-z]+(\s+[a-z]+)+$/; // {{unrestricted double}} {{ double }}
+const idlPrimitiveRegex = /^[a-z]+(\s+[a-z]+)+\??$/; // {{unrestricted double?}} {{ double }}
 const exceptionRegex = /\B"([^"]*)"\B/; // {{ "SomeException" }}
 const methodRegex = /(\w+)\((.*)\)$/;
 const slotRegex = /^\[\[(\w+)\]\]$/;
 // matches: `value` or `[[value]]`
 // NOTE: [[value]] is actually a slot, but database has this as type="attribute"
 const attributeRegex = /^((?:\[\[)?(?:\w+)(?:\]\])?)$/;
+const baseRegex = /^(?:\w+)\??$/;
 const enumRegex = /^(\w+)\["([\w- ]*)"\]$/;
 // TODO: const splitRegex = /(?<=\]\]|\b)\./
 // https://github.com/w3c/respec/pull/1848/files#r225087385
@@ -21,6 +22,7 @@ const methodSplitRegex = /\.?(\w+\(.*\)$)/;
  * @property {"base"} type
  * @property {string} identifier
  * @property {boolean} renderParent
+ * @property {boolean} nullable
  * @property {InlineIdl | null} [parent]
  *
  * @typedef {object} IdlAttribute
@@ -56,6 +58,7 @@ const methodSplitRegex = /\.?(\w+\(.*\)$)/;
  *
  * @typedef {object} IdlPrimitive
  * @property {"idl-primitive"} type
+ * @property {boolean} nullable
  * @property {string} identifier
  * @property {boolean} renderParent
  * @property {InlineIdl | null} [parent]
@@ -116,12 +119,21 @@ function parseInlineIDL(str) {
       continue;
     }
     if (idlPrimitiveRegex.test(value)) {
-      results.push({ type: "idl-primitive", identifier: value, renderParent });
+      const nullable = value.endsWith("?");
+      const identifier = nullable ? value.slice(0, -1) : value;
+      results.push({
+        type: "idl-primitive",
+        identifier,
+        renderParent,
+        nullable,
+      });
       continue;
     }
     // base, always final token
-    if (attributeRegex.test(value) && tokens.length === 0) {
-      results.push({ type: "base", identifier: value, renderParent });
+    if (baseRegex.test(value) && tokens.length === 0) {
+      const nullable = value.endsWith("?");
+      const identifier = nullable ? value.slice(0, -1) : value;
+      results.push({ type: "base", identifier, renderParent, nullable });
       continue;
     }
     throw new SyntaxError(`IDL micro-syntax parsing error in \`{{ ${str} }}\``);
@@ -139,10 +151,13 @@ function parseInlineIDL(str) {
  */
 function renderBase(details) {
   // Check if base is a local variable in a section
-  const { identifier, renderParent } = details;
+  const { identifier, renderParent, nullable } = details;
   if (renderParent) {
-    return html`<a data-xref-type="_IDL_" data-link-type="idl"
-      ><code>${identifier}</code></a
+    return html`<a
+      data-xref-type="_IDL_"
+      data-link-type="idl"
+      data-lt="${identifier}"
+      ><code>${identifier + (nullable ? "?" : "")}</code></a
     >`;
   }
 }
@@ -244,12 +259,13 @@ function renderException(details) {
  * @param {IdlPrimitive} details
  */
 function renderIdlPrimitiveType(details) {
-  const { identifier } = details;
+  const { identifier, nullable } = details;
   const element = html`<a
     data-link-type="idl"
     data-cite="WebIDL"
     data-xref-type="interface"
-    ><code>${identifier}</code></a
+    data-lt="${identifier}"
+    ><code>${identifier + (nullable ? "?" : "")}</code></a
   >`;
   return element;
 }
diff --git a/src/core/inlines.js b/src/core/inlines.js
index 72fd63d45b..544ca15817 100644
--- a/src/core/inlines.js
+++ b/src/core/inlines.js
@@ -61,7 +61,7 @@ const l10n = getIntlData(localizationStrings);
 // TODO: Replace (?!`) at the end with (?:<!`) at the start when Firefox + Safari
 // add support.
 const inlineCodeRegExp = /(?:`[^`]+`)(?!`)/; // `code`
-const inlineIdlReference = /(?:{{[^}]+}})/; // {{ WebIDLThing }}
+const inlineIdlReference = /(?:{{[^}]+\?*}})/; // {{ WebIDLThing }}, {{ WebIDLThing? }}
 const inlineVariable = /\B\|\w[\w\s]*(?:\s*:[\w\s&;<>]+\??)?\|\B/; // |var : Type?|
 const inlineCitation = /(?:\[\[(?:!|\\|\?)?[\w.-]+(?:|[^\]]+)?\]\])/; // [[citation]]
 const inlineExpansion = /(?:\[\[\[(?:!|\\|\?)?#?[\w-.]+\]\]\])/; // [[[expand]]]
diff --git a/tests/spec/core/inlines-spec.js b/tests/spec/core/inlines-spec.js
index 1680405959..65a6394ee3 100644
--- a/tests/spec/core/inlines-spec.js
+++ b/tests/spec/core/inlines-spec.js
@@ -530,6 +530,56 @@ describe("Core - Inlines", () => {
     );
   });
 
+  it("supports {{ Nullable? }} types and primitives", async () => {
+    const body = `
+      <section>
+        <pre class="idl">
+        [Exposed=Window]
+        interface InterFace{};
+        dictionary Dict{};
+        </pre>
+        <p id="interface">{{ InterFace? }}</p>
+        <p id="dictionary">{{ Dict? }}</p>
+        <p id="primitive">{{ unsigned short? }}</p>
+      </section>
+    `;
+    const config = { xref: ["WebIDL"] };
+    const doc = await makeRSDoc(makeStandardOps(config, body));
+
+    const [interfaceDfn, dictDfn] = doc.querySelectorAll(".idl dfn");
+
+    // {{ Interface? }}
+    const interfaceAnchor = doc.querySelector("#interface a");
+    expect(interfaceAnchor.textContent).toBe("InterFace?");
+    expect(interfaceAnchor.hash.endsWith(interfaceDfn.id)).toBeTrue();
+
+    const interfaceData = interfaceAnchor.dataset;
+    expect(interfaceData.xrefType).toBe("_IDL_");
+    expect(interfaceData.linkType).toBe("idl");
+    expect(interfaceData.lt).toBe("InterFace");
+
+    // {{ Dict? }}
+    const dictAnchor = doc.querySelector("#dictionary a");
+    expect(dictAnchor.textContent).toBe("Dict?");
+    expect(dictAnchor.hash.endsWith(dictDfn.id)).toBeTrue();
+
+    const dictData = dictAnchor.dataset;
+    expect(dictData.xrefType).toBe("_IDL_");
+    expect(dictData.linkType).toBe("idl");
+    expect(dictData.lt).toBe("Dict");
+
+    // {{ unsigned short? }}
+    const primitiveAnchor = doc.querySelector("#primitive a");
+    expect(primitiveAnchor.textContent).toBe("unsigned short?");
+    expect(primitiveAnchor.hash).toBe("#idl-unsigned-short");
+
+    const primitiveData = primitiveAnchor.dataset;
+    expect(primitiveData.linkType).toBe("idl");
+    expect(primitiveData.cite).toBe("webidl");
+    expect(primitiveData.xrefType).toBe("interface");
+    expect(primitiveData.lt).toBe("unsigned short");
+  });
+
   it("doesn't link processed inline WebIDL if inside a definition", async () => {
     const body = `
       <section>