Stop defining volumechange in terms of public API

cf4109f made it so that technically the muted content attribute and playing backwards would result in a volumechange event. That was not intentional. This restores those aspects to before that commit and also modernizes the editorial style of the concepts involved.

Author: annevk

source

@@ -43366,14 +43366,41 @@ red:89
   Initially, the volume should be 1.0, but user agents may remember the last set value across
   sessions, on a per-site basis or otherwise, so the volume may start at other values.</p>
 
+  <div algorithm>
+  <p>To <dfn export>set the playback volume</dfn> of a <span>media element</span>
+  <var>element</var> to a number <var>value</var>:</p>
+
+  <ol>
+   <li><p>If <var>element</var>'s <span data-x="concept-media-volume">playback volume</span> equals
+   <var>value</var>, then return.</p></li>
+
+   <li><p>Set <var>element</var>'s <span data-x="concept-media-volume">playback volume</span> to
+   <var>value</var>.</p></li>
+
+   <li><p>If <var>element</var> is not <span>allowed to play</span>, then run the <span>internal
+   pause steps</span> for <var>element</var>.</p></li>
+
+   <li><p><span>Queue a media element task</span> given <var>element</var> to <span
+   data-x="concept-event-fire">fire an event</span> named <code
+   data-x="event-media-volumechange">volumechange</code> at <var>element</var>.</p></li>
+  </ol>
+  </div>
+
   <div algorithm>
   <p>The <dfn attribute for="HTMLMediaElement"><code data-x="dom-media-volume">volume</code></dfn>
-  IDL attribute must return the <span data-x="concept-media-volume">playback volume</span> of any
-  audio portions of the <span>media element</span>. On setting, if the new value is in the range 0.0
-  to 1.0 inclusive, the <span>media element</span>'s <span data-x="concept-media-volume">playback
-  volume</span> must be set to the new value. If the new value is outside the range 0.0 to 1.0
-  inclusive, then, on setting, an <span>"<code>IndexSizeError</code>"</span>
-  <code>DOMException</code> must be thrown instead.</p>
+  getter steps are to return <span>this</span>'s <span data-x="concept-media-volume">playback
+  volume</span>.</p>
+  </div>
+
+  <div algorithm>
+  <p>The <code data-x="dom-media-volume">volume</code> setter steps are:</p>
+
+  <ol>
+   <li><p>If the given value is not in the range 0.0 to 1.0 inclusive, then throw an
+   <span>"<code>IndexSizeError</code>"</span> <code>DOMException</code>.</p></li>
+
+   <li><p><span>Set the playback volume</span> of <span>this</span> to the given value.</p></li>
+  </ol>
   </div>
 
   <p>A <span>media element</span> is <dfn for="media element" data-x="concept-media-muted"
@@ -43394,29 +43421,39 @@ red:89
 
   <p>Each <span>media element</span> has a <dfn data-x="concept-media-muted-state">muted
   state</dfn>, which is either true, false, or "<code data-x="">default</code>"; it is initially "<code
-  data-x="">default</code>". User agents may set a <span>media element</span>'s <span
-  data-x="concept-media-muted-state">muted state</span> to true or false (e.g., remembering the last
-  set value across sessions, on a per-site basis or otherwise).</p>
+  data-x="">default</code>". User agents may <span>set the muted state</span> of a <span>media
+  element</span> to true or false (e.g., remembering the last set value across sessions, on a
+  per-site basis or otherwise).</p>
 
   <div algorithm>
-  <p>The <dfn attribute for="HTMLMediaElement"><code data-x="dom-media-muted">muted</code></dfn>
-  getter steps are to return true if this is <span
-  data-x="concept-media-muted">muted</span>; otherwise false.</p>
+  <p>To <dfn export>set the muted state</dfn> of a <span>media element</span> <var>element</var> to
+  a boolean <var>value</var>:</p>
+
+  <ol>
+   <li><p>If <var>element</var>'s <span data-x="concept-media-muted-state">muted state</span>
+   equals <var>value</var>, then return.</p></li>
+
+   <li><p>Set <var>element</var>'s <span data-x="concept-media-muted-state">muted state</span> to
+   <var>value</var>.</p></li>
+
+   <li><p>If <var>element</var> is not <span>allowed to play</span>, then run the <span>internal
+   pause steps</span> for <var>element</var>.</p></li>
+
+   <li><p><span>Queue a media element task</span> given <var>element</var> to <span
+   data-x="concept-event-fire">fire an event</span> named <code
+   data-x="event-media-volumechange">volumechange</code> at <var>element</var>.</p></li>
+  </ol>
   </div>
 
   <div algorithm>
-  <p>The <code data-x="dom-media-muted">muted</code> setter steps are to set this's
-  <span data-x="concept-media-muted-state">muted state</span> to the given value.</p>
+  <p>The <dfn attribute for="HTMLMediaElement"><code data-x="dom-media-muted">muted</code></dfn>
+  getter steps are to return true if <span>this</span> is <span
+  data-x="concept-media-muted">muted</span>; otherwise false.</p>
   </div>
 
   <div algorithm>
-  <p>Whenever either of the values that would be returned by the <code
-  data-x="dom-media-volume">volume</code> and <code data-x="dom-media-muted">muted</code> IDL
-  attributes change, the user agent must <span>queue a media element task</span> given the
-  <span>media element</span> to <span data-x="concept-event-fire">fire an event</span> named <code
-  data-x="event-media-volumechange">volumechange</code> at the <span>media element</span>. Then, if
-  the <span>media element</span> is not <span>allowed to play</span>, the user agent must run the
-  <span>internal pause steps</span> for the <span>media element</span>.</p>
+  <p>The <code data-x="dom-media-muted">muted</code> setter steps are to <span>set the muted
+  state</span> of <span>this</span> to the given value.</p>
   </div>
 
   <p>A user agent has an associated <dfn>volume locked</dfn> (a boolean). Its value is