Make module scripts modify less global script state

They set document.currentScript to null, and no longer fire
beforescriptexecute and afterscriptexecute events.

Closes #997. See #1013 for a future alternative to
document.currentScript, and #943 for more discussion of the events.

source

@@ -9053,12 +9053,14 @@ partial /*sealed*/ interface <dfn>Document</dfn> {
    <dd>
 
     <p>Returns the <code>script</code> element, or the <span>SVG <code>script</code></span> element,
-    that is currently executing. In the case of reentrant script execution, returns the one that
-    most recently started executing amongst those that have not yet finished executing.</p>
+    that is currently executing, as long as the element represents a <span>classic script</span>.
+    In the case of reentrant script execution, returns the one that most recently started executing
+    amongst those that have not yet finished executing.</p>
 
     <p>Returns null if the <code>Document</code> is not currently executing a <code>script</code>
     or <span>SVG <code>script</code></span> element (e.g., because the running script is an event
-    handler, or a timeout).</p>
+    handler, or a timeout), or if the currently executing <code>script</code> or <span>SVG
+    <code>script</code></span> element represents a <span>module script</span>.</p>
 
    </dd>
 
@@ -9067,9 +9069,9 @@ partial /*sealed*/ interface <dfn>Document</dfn> {
   <div w-nodev>
 
   <p>The <dfn><code data-x="dom-document-currentScript">currentScript</code></dfn> attribute, on
-  getting, must return the value to which it was most recently initialised. When the
-  <code>Document</code> is created, the <code
-  data-x="dom-document-currentScript">currentScript</code> must be initialised to null.</p>
+  getting, must return the value to which it was most recently set. When the <code>Document</code>
+  is created, the <code data-x="dom-document-currentScript">currentScript</code> must be
+  initialised to null.</p>
 
   </div>
 
@@ -59012,7 +59014,8 @@ o............A....e
 
    <li>
 
-    <p><span>Fire a simple event</span> named <code
+    <p>If <span data-x="concept-script-type">the script's type</span> is "<code
+    data-x="">classic</code>", <span>fire a simple event</span> named <code
     data-x="event-beforescriptexecute">beforescriptexecute</code> that bubbles and is cancelable
     at the <code>script</code> element.</p>
 
@@ -59035,22 +59038,7 @@ o............A....e
     <p>Let <var>old script element</var> be the value to which the <code>script</code>
     element's <span>node document</span>'s <code
     data-x="dom-document-currentScript">currentScript</code> object was most recently
-    initialised.</p>
-
-   </li>
-
-   <li>
-
-    <p>Initialise the <code>script</code> element's <span>node document</span>'s <code
-    data-x="dom-document-currentScript">currentScript</code> object to the <code>script</code>
-    element.</p>
-
-   </li>
-
-   <li>
-
-    <p>Let <var>settings object</var> be the <span>environment settings object</span> of the
-    <code>script</code> element's <span>node document</span>'s <code>Window</code> object.</p>
+    set.</p>
 
    </li>
 
@@ -59061,23 +59049,34 @@ o............A....e
     <dl class="switch">
      <dt>"<code data-x="">classic</code>"</dt>
      <dd>
-      <p><span data-x="run a classic script">Run the classic script</span> given by <span
-      data-x="concept-script-script">the script's script</span>.</p>
+      <ol>
+       <li><p>Set the <code>script</code> element's <span>node document</span>'s <code
+       data-x="dom-document-currentScript">currentScript</code> attribute to the
+       <code>script</code> element.</p></li>
+
+       <li><p><span data-x="run a classic script">Run the classic script</span> given by <span
+       data-x="concept-script-script">the script's script</span>.</p></li>
+      </ol>
      </dd>
 
      <dt>"<code data-x="">module</code>"</dt>
      <dd>
-      <p><span data-x="run a module script">Run the module script</span> given by <span
-      data-x="concept-script-script">the script's script</span>.</p>
+      <ol>
+       <li><p>Set the <code>script</code> element's <span>node document</span>'s <code
+       data-x="dom-document-currentScript">currentScript</code> attribute to null.</p></li>
+
+       <li><p><span data-x="run a module script">Run the module script</span> given by <span
+       data-x="concept-script-script">the script's script</span>.</p></li>
+      </ol>
      </dd>
     </dl>
 
    </li>
 
    <li>
 
-    <p>Initialise the <code>script</code> element's <span>node document</span>'s <code
-    data-x="dom-document-currentScript">currentScript</code> object to <var>old script
+    <p>Set the <code>script</code> element's <span>node document</span>'s <code
+    data-x="dom-document-currentScript">currentScript</code> attribute to <var>old script
     element</var>.</p>
 
    </li>
@@ -59090,7 +59089,8 @@ o............A....e
 
    <li>
 
-    <p><span>Fire a simple event</span> named <code
+    <p>If <span data-x="concept-script-type">the script's type</span> is "<code
+    data-x="">classic</code>", <span>fire a simple event</span> named <code
     data-x="event-afterscriptexecute">afterscriptexecute</code> that bubbles (but is not
     cancelable) at the <code>script</code> element.</p>