Tweak how accesskey on legend works

Fixes #3950.

Tests: TODO

source

@@ -56939,25 +56939,42 @@ interface <dfn>HTMLDetailsElement</dfn> : <span>HTMLElement</span> {
   <h5><dfn data-x="legend-command">Using the <code data-x="attr-accesskey">accesskey</code> attribute
   on a <code>legend</code> element to define a command</dfn></h5>
 
-  <p>A <code>legend</code> element that has an <span>assigned access key</span> and is a child of a
-  <code>fieldset</code> element that has a descendant that is not a descendant of the
-  <code>legend</code> element and is neither a <code>label</code> element nor a <code>legend</code>
-  element but that <span data-x="concept-command">defines a command</span>, itself <span
-  data-x="concept-command">defines a command</span>.</p>
+  <p>A <code>legend</code> element that has an <span>assigned access key</span> and matches one of
+  the following conditions, itself <span data-x="concept-command">defines a command</span>.</p>
+
+  <ul>
+   <li>The <code>legend</code> is focusable</li>
+
+   <li>The <code>legend</code> is a child of a <code>fieldset</code> element that has a descendant
+   that element and is neither a <code>label</code> element nor a <code>legend</code> element but
+   that <span data-x="concept-command">defines a command</span></li>
+  </ul>
 
   <p>The <span data-x="command-facet-Label">Label</span> of the command is the string given by the
   element's <code>textContent</code> IDL attribute.</p>
 
   <p>The <span data-x="command-facet-AccessKey">Access Key</span> of the command is the element's
   <span>assigned access key</span>.</p>
 
-  <p>The <span data-x="command-facet-HiddenState">Hidden State</span>, <span
+  <p>If the <code>legend</code> element is focusable, then:</p>
+
+  <ul>
+   <li><p>The <span data-x="command-facet-HiddenState">Hidden State</span> is true (hidden) if the
+   element has a <code data-x="attr-hidden">hidden</code> attribute, and false otherwise.</p></li>
+
+   <li><p>The <span data-x="command-facet-DisabledState">Disabled State</span> of the command is
+   true if it or one of its ancestors is <span>inert</span>, and false otherwise.</p></li>
+
+   <li><p>The <span data-x="command-facet-Action">Action</span> is to run the <span>focusing
+   steps</span> for the element.</p></li>
+  </ul>
+
+  <p>Otherwise, the <span data-x="command-facet-HiddenState">Hidden State</span>, <span
   data-x="command-facet-DisabledState">Disabled State</span>, and <span
   data-x="command-facet-Action">Action</span> facets of the command are the same as the respective
   facets of the first element in <span>tree order</span> that is a descendant of the parent of the
-  <code>legend</code> element that <span data-x="concept-command">defines a command</span> but is not
-  a descendant of the <code>legend</code> element and is neither a <code>label</code> nor a
-  <code>legend</code> element.</p>
+  <code>legend</code> element that <span data-x="concept-command">defines a command</span> but is
+  neither a <code>label</code> nor a <code>legend</code> element.</p>
 
 
   <h5><dfn data-x="accesskey-command">Using the <code data-x="attr-accesskey">accesskey</code>