Add Presentation to DL in Accordion Example

modified:   examples/accordion/accordion1.html to address feedback in issue #210 from @jasonkiss:
1. Added role `presentation` to the `dl` element.
2. Added a row to the states and properties table for the presentation role.
3. Revised the `heading` row of the states and properties table.
4. Revised the `aria-level` row of the states and properties table.

examples/accordion/accordion1.html

@@ -34,7 +34,7 @@ <h2 id="ex_label">Example</h2>
     <div role="separator" id="ex_start_sep" aria-labelledby="ex_start_sep ex_label" aria-label="Start of"></div>
     <div id="coding-arena">
       <div class="demo-block">
-        <dl id="accordionGroup">
+        <dl id="accordionGroup" role="presentation">
           <dt role="heading" aria-level="3" class="clearfix">
             <a role="button" aria-expanded="false" href="#" class="accAccordion"
               aria-controls="sect1" data-defaultopen="true" id="accordion1id"
@@ -182,30 +182,39 @@ <h2 id="rps_label">Role, Property, State, and Tabindex  Attributes</h2>
       </thead>
       <tbody>
         <tr>
-          <th scope="row"><code>heading</code></th>
+          <th scope="row"><code>presentation</code></th>
           <td></td>
-          <td><code>dt</code></td>
+          <td><code>dl</code></td>
           <td>
             <ul>
-              <li>Creates the accordion header.</li>
-              <li>The accordion structure is built on an HTML definition list where each term is recast as a header and each definition is recast as a panel.</li>
+              <li>Indicates that the <code>dl</code> element is being used to control presentation and does not represent a definition list.</li>
+              <li>This implementation uses an HTML definition list where each term is recast as a header and each definition is recast as a region that contains panel content.</li>
             </ul>
           </td>
         </tr>
+        <tr>
+          <th scope="row"><code>heading</code></th>
+          <td></td>
+          <td><code>dt</code></td>
+          <td>Identifies the element as a heading that serves as an accordion header.</td>
+        </tr>
         <tr>
           <td></td>
           <th scope="row"><code>aria-level=<q>3</q></code></th>
           <td><code>dt</code></td>
           <td>
-              Specifies heading level for the accordion header.
+            <ul>
+              <li>Specifies heading level for the accordion header.</li>
+              <li>Level 3 is chosen because the accordion is contained in a section with a level 2 heading.</li>
+            </ul>
           </td>
         </tr>
         <tr>
           <th scope="row"><code>button</code></th>
           <td></td>
           <td><code>a</code></td>
           <td>
-            A button inside the accordion header that provides hide/show functionality.
+            Identifies the element as a button inside the accordion header that provides hide/show functionality.
           </td>
         </tr>
         <tr>