treeitems can omit groups by explicit aria-level

index.html

@@ -9976,7 +9976,7 @@ <h5>Presentational Role Inheritance</h5>
 			<rdef>treeitem</rdef>
 			<div class="role-description">
 				<p>An item in a <rref>tree</rref>.</p>
-        				<p>A <rref>treeitem</rref> <a>element</a> can contain a sub-level group of elements that can be expanded or collapsed. An expandable collection of <code>treeitem</code> elements are enclosed in an element with the <rref>group</rref> <a>role</a>.</p>
+				<p>A <rref>treeitem</rref> <a>element</a> can contain a sub-level group of elements that can be expanded or collapsed. An expandable collection of <code>treeitem</code> elements are usually enclosed in an element with the <rref>group</rref> <a>role</a>.</p>
 				<p>Authors MUST ensure [=elements=] with <a>role</a> <code>treeitem</code> are <a>accessibility children</a> of an element with role <rref>tree</rref> or an element with role <rref>group</rref> that is the <a>accessibility child</a> of an element with role <rref>treeitem</rref>.</p>
         <p>In certain conditions, a user agent MAY provide an implicit value for <sref>aria-selected</sref> for each <rref>treeitem</rref> in a <rref>tree</rref>, and if it does, the user agent MUST ensure the following conditions are met before providing an implicit value:</p>
         <ul>
@@ -9997,6 +9997,12 @@ <h5>Presentational Role Inheritance</h5>
           <li>The user interface makes the meaning and purpose of each state apparent.</li>
           <li>The user interface provides a separate method for controlling each state.</li>
         </ul>
+		<p>
+			User agents MUST calculate an implicit value for <sref>aria-level</sref> from the document structure if the author does not explicitly specify a value.
+		</p>
+		<p>
+			Authors MAY omit using nested <rref>group</rref> elements to indicate level hierarchy. When doing so, authors MUST ensure all <rref>treeitem</rref> elements in the <rref>tree</rref> have explicit values for <sref>aria-level</sref>, <sref>aria-posinset</sref>, and <sref>aria-setsize</sref>.
+		</p>
 			</div>
 			<table class="role-features">
 				<caption>Characteristics:</caption>