Editorial: Clarify AX Tree Exclusion for Children Presentational True…

… in Core-AAM (#647)

Clarify the criteria for elements with children presentational true to specify that:
1. Text content of excluded elements is included
2. Exceptions, such as focusability, also apply

This is already stated in the ARIA specification, but was not clear from
the text present in the Core AAM.

Fixes github issue #492.

core-aam/core-aam.html

@@ -468,7 +468,9 @@ <h4>Excluding Elements from the Accessibility Tree</h4>
 	    <p>If not already excluded from the accessibility tree per the above rules,   user agents SHOULD NOT include the following elements in the   accessibility tree: </p>
 	    <ul>
 	      <li>Elements, including their descendants, that have a <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> global attribute of <a class="property-reference" href="#aria-hidden"><code>aria-hidden</code></a><code>=&quot;true&quot;.</code> In other words, <code>aria-hidden=&quot;true&quot;</code> on a parent overrides <code>aria-hidden=&quot;false&quot;</code> on descendants. </li>
-	      <li>Children of <a class="termref">objects</a> which have the characteristic &quot;<a class="specref" href="#childrenArePresentational">Children Presentational: True</a>&quot;:
+        <li>
+          <p>Any descendants of elements that have the characteristic &quot;<a class="specref" href="#childrenArePresentational">Children Presentational: True</a>&quot; unless the descendant is not allowed to be presentational because it meets one of the conditions for exception described in <a class="specref" href="#conflict_resolution_presentation_none">Presentational Roles Conflict Resolution</a> in <cite><a class="specref" href="#">Accessible Rich Internet Applications (WAI-ARIA) 1.1</a></cite> [[!WAI-ARIA]]. However, the text content of any excluded descendants is included.</p>
+          <p>Elements having one of the following roles have the characteristic &quot;<a class="specref" href="#childrenArePresentational">Children Presentational: True</a>&quot;:</p>
 	        <ul>
 	          <li><a class="role-reference" href="#button"><code>button</code></a></li>
 	          <li><a class="role-reference" href="#checkbox"><code>checkbox</code></a></li>