fix inconsistency nits (#269)

index.html

@@ -1395,7 +1395,7 @@ <h3>HTML Element Role Mappings</h3>
  <td class="ax"><div class="general">Use WAI-ARIA mapping</div></td>
  <td class="comments"></td>
  </tr>
- <tr id="el-header2" tabindex="-1">
+ <tr tabindex="-1" id="el-form-no-accessible-name">
  <th>
  <a data-cite="HTML">`form`</a> without an <a class="termref">accessible name</a>
  </th>
@@ -1609,7 +1609,7 @@ <h3>HTML Element Role Mappings</h3>
  <td class="ax"><div class="general">Use WAI-ARIA mapping</div></td>
  <td class="comments"></td>
  </tr>
- <tr tabindex="-1" id="el-img-emptyalt">
+ <tr tabindex="-1" id="el-img-empty-alt">
  <th><a href="https://www.w3.org/TR/html/semantics-embedded-content.html#the-img-element"><code>img</code></a> <span class="el-context">(<a href="https://www.w3.org/TR/html/semantics-embedded-content.html#element-attrdef-img-alt"><code>alt</code></a> attribute value is an empty string, i.e. <code>alt=""</code> or <code>alt</code> with no value in the markup)</span></th>
  <td class="aria">
  <div class="role"><a class="core-mapping" href="#role-map-presentation"><code>presentation</code></a></div>
@@ -2652,7 +2652,7 @@ <h3>HTML Element Role Mappings</h3>
  <td class="ax"><div class="general">Not mapped</div></td>
  <td class="comments"></td>
  </tr>
- <tr id="el-picture" tabindex="-1">
+ <tr tabindex="-1" id="el-picture">
  <th><a data-cite="HTML">`picture`</a></th>
  <td class="aria">No corresponding role</td>
  <td class="ia2"><div class="general">Not mapped</div></td>