Corrected Label Attribute Documentation for File Directory Treeview Examples

For issue #223, modified examples/treeview/treeview-1/treeview-1a.html:
1. Added bullet describing tree role to the tree row of the roles, states, and properties table.
2. In roles, states, and properties table, corrected the row for label  of the tree element: changed from aria-label to aria-labelledby to reflect the example code.

For issue #224, Modified examples/treeview/treeview-1/treeview-1b.html:
1. Added bullet describing tree role to the tree row of the roles, states, and properties table.
2. In roles, states, and properties table, corrected the row for label  of the tree element: changed from aria-label to aria-labelledby to reflect the example code.

Author: mcking65

examples/treeview/treeview-1/treeview-1a.html

@@ -388,8 +388,9 @@ <h2 id="rps_label">Role, Property, State, and Tabindex  Attributes</h2>
               <td>
                 <ul>
                   <li>Identifies the <code>ul</code> element as an <code>tree</code> widget.</li>
+                  <li>A <code>tree</code> is a container widget for focusable, interactive <code>treeitem</code> elements.</li>
                   <li>
-                    Is not made focusable with a <code>tabindex</code> value because a 
+                    The <code>tree</code> is not made focusable with a <code>tabindex</code> value because a 
                     <a href="../../../#kbd_roving_tabindex">roving tabindex</a> 
                     is used to control which descendant <code>treeitem</code> receives focus.
                   </li>
@@ -398,11 +399,9 @@ <h2 id="rps_label">Role, Property, State, and Tabindex  Attributes</h2>
             </tr>
             <tr>
               <td></td>
-              <th scope="row"><code>aria-label=&quot;<em>string</em>&quot;</code></th>
+              <th scope="row"><code>aria-labelledby=&quot;IDREF&quot;</code></th>
               <td><code>ul</code></td>
-              <td>
-                Defines an accessible name, i.e., label, that identifies the purpose of the <code>tree</code>.
-              </td>
+              <td>Refers to the heading element that contains the label that identifies the purpose of the <code>tree</code>.</td>
             </tr>
             <tr>
               <th scope="row"><code>treeitem</code></th>

examples/treeview/treeview-1/treeview-1b.html

@@ -547,8 +547,9 @@ <h2 id="rps_label">Role, Property, State, and Tabindex  Attributes</h2>
               <td>
                 <ul>
                   <li>Identifies the <code>ul</code> element as an <code>tree</code> widget.</li>
+                  <li>A <code>tree</code> is a container widget for focusable, interactive <code>treeitem</code> elements.</li>
                   <li>
-                    Is not made focusable with a <code>tabindex</code> value because a 
+                    The <code>tree</code> is not made focusable with a <code>tabindex</code> value because a 
                     <a href="../../../#kbd_roving_tabindex">roving tabindex</a> 
                     is used to control which descendant <code>treeitem</code> receives focus.
                   </li>
@@ -557,11 +558,9 @@ <h2 id="rps_label">Role, Property, State, and Tabindex  Attributes</h2>
             </tr>
             <tr>
               <td></td>
-              <th scope="row"><code>aria-label=&quot;<em>string</em>&quot;</code></th>
+              <th scope="row"><code>aria-labelledby=&quot;IDREF&quot;</code></th>
               <td><code>ul</code></td>
-              <td>
-                Defines an accessible name, i.e., label, that identifies the purpose of the <code>tree</code>.
-              </td>
+              <td>Refers to the heading element that contains the label that identifies the purpose of the <code>tree</code>.</td>
             </tr>
             <tr>
               <th scope="row"><code>treeitem</code></th>