ion
        feature should document the reason for not implementing the feature.
      </li>
	  </ul>
	</li>
</ol>
<p>
  Feature status is in practice indicated by
  <a href="https://tools.ietf.org/html/rfc2119">RFC&nbsp;2119</a> assertions
  associated with the feature.  Features defined using any assertions
  containing the words MUST are considered required.
  Features defined using MAY and SHOULD assertions are considered optional.
</p>

<h4 id="h_NotesOnTesting"><a id="NotesOnTesting" name="NotesOnTest