Combobox: Revise UA, AT, and checker guidance per agreed text in issu…

…e 1178 (#1223)

* Revise UA, AT, and checker guidance per agreed text in issue 1178
* Remove normative requirements related to ARIA 1.0 and ARIA 1.1 patterns as suggested by @cookiecrook
* described in -> defined by

index.html

@@ -2154,14 +2154,16 @@ <h2>Definition of Roles</h2>
  		  <p class="ednote" title="Validity changes combobox for ARIA 1.2">
 			   Please review the following carefully. As a result of these changes a combobox following the ARIA 1.1 combobox specification will no longer conform with the ARIA specification.
 		  </p>
-		  <p>
-			The ARIA 1.0 specification describes a <code>combobox</code> pattern where the input element with the <code>combobox</code> role references the popup element with <pref>aria-owns</pref> instead of <pref>aria-controls</pref>.
-			<a>User agents</a>, <a>assistive technologies</a>, and conformance checkers SHOULD continue to support the ARIA 1.0 pattern so that existing implementations of the ARIA 1.0 pattern remain functional.
-			The ARIA 1.1 specification describes a <code>combobox</code> pattern where the element with role <code>combobox</code> is a composite container instead of a focusable input.
-			<a>User agents</a> and <a>assistive technologies</a> did not adequately support the ARIA 1.1 pattern, so the ARIA 1.2 pattern supersedes the ARIA 1.1 pattern, which authors SHOULD abandon. 
-		  </p>
-				<p>The features and behaviors of combobox implementations vary widely. Consequently, there are many important authoring considerations. See the <cite><a href="" class="practices"><abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> Authoring Practices</a></cite> for additional details on implementing combobox design patterns.</p>
-			</div>
+        <div class="note">
+          <p>The structural requirements  for <code>combobox</code> defined by this version of the specification are different from the requirements defined by ARIA 1.0 and ARIA 1.1:</p>
+          <ul>
+            <li>The ARIA 1.0 specification required the input element with the <code>combobox</code> role to be a single-line text field and reference the popup element with <pref>aria-owns</pref> instead of <pref>aria-controls</pref>.</li>
+            <li>The ARIA 1.1 specification, which was not broadly supported by assistive technologies, required the <code>combobox</code> to be a non-focusable element with two required owned elements -- a focusable <rref>textbox</rref> and a popup element controlled by the <rref>textbox</rref>.</li>
+            <li>The changes introduced in ARIA 1.2 improve interoperability with assistive technologies and enable authors to create presentations of combobox that more closely imitate a native HTML <code>select</code> element.</li>
+          </ul>
+        </div>
+        <p>The features and behaviors of combobox implementations vary widely. Consequently, there are many important authoring considerations. See the <cite><a href="" class="practices"><abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> Authoring Practices</a></cite> for additional details on implementing combobox design patterns.</p>      
+      </div>
 			<table class="role-features">
 				<caption>Characteristics:</caption>
 				<thead>