fix(aria-level): update to specify only level 1-6 (#1873)

Closes #1050 

Related APG Issue/PR: w3c/aria-practices#2620

index.html

@@ -12026,6 +12026,8 @@ <h2>Definitions of States and Properties (all aria-* attributes)</h2>
 				<p>This attribute is applied to elements that act as leaf nodes within the orientation of the set, for example, on elements with role <rref>treeitem</rref> rather than elements with role <rref>group</rref>. This means that multiple elements in a set may have the same value for this attribute. Although it would be less repetitive to provide a single value on the container, restricting this to leaf nodes ensures that there is a single way for <a>assistive technologies</a> to use the attribute.</p>
 				<p>If the <abbr title="Document Object Model">DOM</abbr> ancestry accurately represents the level, the <a>user agent</a> can calculate the level of an item from the document structure. This attribute can be used to provide an explicit indication of the level when that is not possible to calculate from the document structure or the <pref>aria-owns</pref> attribute. User agent support for automatic calculation of level may vary; authors SHOULD test with [=user agents=] and assistive technologies to determine whether this attribute is needed. If the author intends for the user agent to calculate the level, the author SHOULD omit this attribute.</p>
                 <p class="note"> In the case of a <rref>treegrid</rref>, <pref>aria-level</pref> is supported on elements with the role <rref>row</rref>, not elements with role <rref>gridcell</rref>. At first glance, this may seem inconsistent with the application of <pref>aria-level</pref> on <rref>treeitem</rref> elements, but it is consistent in that the <rref>row</rref> acts as the leaf node within the vertical orientation of the <rref>grid</rref>, whereas the <rref>gridcell</rref> is a leaf node within the horizontal orientation of each <rref>row</rref>. Level is not supported on sets of cells within rows, so the <pref>aria-level</pref> attribute is applied to the element with the role <rref>row</rref>.</p>
+<p class="note">On elements with role <pref>heading</pref>, values for <pref>aria-level</pref> above 6 can create difficulties for users. Also, at the time of this writing, most combinations of user agents and assistive technologies only support <pref>aria-level</pref> integers 1-9 on headings. See the [WAI-ARIA Authoring Practices](https://w3c.github.io/aria-practices/) for additional guidance on <pref>aria-level</pref>.</p>
+
 			</div>
 			<table class="property-features">
 				<caption>Characteristics:</caption>