Allow treeitems to omit groups by specifiying aria-level, aria-posinset, and aria-setsize

accname/index.html

@@ -628,7 +628,8 @@ <h4>Computation steps</h4>
                 <li id="comp_host_language_label">
                   <span id="step2E"><!-- Don't link to this legacy numbered ID. --></span><em>Host Language Label:</em> Otherwise, if the <code>current node</code>'s native markup provides an
                   [=attribute=] (e.g. <code>alt</code>) or [=element=] (e.g. HTML <code>label</code> or SVG <code>title</code>) that defines a text alternative, return that alternative in the form of
-                  a <code>flat string</code> as defined by the host language, unless the <code>current node</code> is exposed as presentational (<code>role="presentation"</code> or <code>role="none"</code>).
+                  a <code>flat string</code> as defined by the host language, unless the <code>current node</code> is exposed as presentational (<code>role="presentation"</code> or
+                  <code>role="none"</code>).
                   <div class="note">
                     See <a href="https://www.w3.org/TR/html-aam-1.0/#accessible-name-and-description-computation">HTML-AAM</a>,
                     <a href="https://www.w3.org/TR/svg-aam-1.0/#mapping_additional_nd">SVG-AAM</a>, or other host language documentation for more information on markup that defines a text alternative.

index.html

@@ -11569,13 +11569,18 @@ <h5>Presentational Role Inheritance</h5>
           <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
+              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>
+              Authors MAY use nested <rref>group</rref> elements to implicitly indicate level hierarchy. Otherwise, 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>
+            <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>
               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: