Clarify when an element is disabled (w3c#1807)

Selenium's atom "Is Element Enabled" special-cases the
disabled state for "option" and "optgroup" elements
when the nearest anchestor "select" is disabled as well.

index.html

@@ -4505,8 +4505,8 @@ <h2>Elements</h2>
 <dl class=subcategories>
  <dt><dfn data-lt="mutable form control element">Mutable form control elements</dfn>
  <dd><p>Denotes [^input^] elements
-  that are <a>mutable</a> (e.g. that are not <a>read only</a> or <a>actually disabled</a>)
-  and whose [^input/type^] attribute
+  that are <a>mutable</a> (e.g. that are not <a>read only</a> or
+  <a>disabled</a>) and whose [^input/type^] attribute
   is in one of the following states:
 
   <ul class=brief>
@@ -4603,6 +4603,22 @@ <h3>Interactability</h3>
  <li><p>Return the pair of (<var>x</var>, <var>y</var>).
 </ol>
 
+<p>An <a>element</a> |element| is <dfn>disabled</dfn> if the following steps
+ return true:
+
+<ol>
+ <li><p>If |element| is an <a>option</a> element or |element| is an <a>optgroup</a> element:
+  <ol>
+   <li><p>For each [=tree/inclusive ancestor=] |ancestor| of |element|:
+    <ol>
+     <li><p>If |ancestor| is an <a>optgroup</a> element or |ancestor| is a <a>select</a>
+      element, and |ancestor| is [=actually disabled=], return true.
+    </ol>
+   <li><p>Return false.
+  </ol>
+ <li><p>Return |element| is [=actually disabled=].
+</ol>
+
 <p>An <a>element</a> is <dfn>in view</dfn>
  if it is a member of its own <a>pointer-interactable paint tree</a>,
  given the pretense that its <a>pointer events are not disabled</a>.
@@ -5912,7 +5928,7 @@ <h4><dfn>Is Element Enabled</dfn></h4>
   <p>Otherwise, let <var>enabled</var> to false
    and jump to the last step of this algorithm.
 
- <li><p>Set <var>enabled</var> to false if a form control is <a>actually disabled</a>.
+ <li><p>Set <var>enabled</var> to false if a form control is <a>disabled</a>.
 
  <li><p>Return <a>success</a> with data <var>enabled</var>.
 </ol>
@@ -6099,7 +6115,7 @@ <h4><dfn>Element Click</dfn></h4>
 
        <li><p>Run the <a>focusing steps</a> on <var>parent node</var>.
 
-       <li><p>If <var>element</var> is not <a>actually disabled</a>:
+       <li><p>If <var>element</var> is not <a>disabled</a>:
 
         <ol>
          <li><p>[=fire an event|Fire=] an <a><code>input</code></a> event at <var>parent node</var>.