Remove implicit value of aria-level from heading role (#942)

* Remove implicit value from heading role
* Adjust heading role verbiage to reflect aria-level authoring expectations

index.html

@@ -3252,7 +3252,7 @@ <h2>Definition of Roles</h2>
 			<rdef>heading</rdef>
 			<div class="role-description">
 				<p>A heading for a section of the page.</p>
-				<p>Often, <code>heading</code> elements will be referenced with the <pref>aria-labelledby</pref> <a>attribute</a> of the section for which they serve as a heading. If headings are organized into a logical outline, the <pref>aria-level</pref> attribute is used to indicate the nesting level.</p>
+				<p>Often, <code>heading</code> elements will be referenced with the <pref>aria-labelledby</pref> <a>attribute</a> of the section for which they serve as a heading. To ensure headings are organized into a logical outline, authors MUST use the <pref>aria-level</pref> attribute to indicate the proper nesting level.</p>
 			</div>
 			<table class="role-features">
 				<caption>Characteristics:</caption>
@@ -3328,10 +3328,6 @@ <h2>Definition of Roles</h2>
 						<th class="role-presentational-inherited-head" scope="row">Inherits Presentational:</th>
 						<td class="role-presentational-inherited"> </td>
 					</tr>
-					<tr>
-						<th class="implicit-values-head" scope="row">Implicit Value for Role:</th>
-						<td class="implicit-values">Default for <pref>aria-level</pref> is <code class="default">2</code>.</td>
-					</tr>
 				</tbody>
 			</table>
 		</div>