acters</li>
      <li>
<a href="terminology.html#must-requirement" id="must-requirement_xref39">must</a>
      not contain permanently undefined Unicode characters</li>
      <li>
<a href="terminology.html#must-requirement" id="must-requirement_xref40">must</a>
      not contain control characters other than
        <a href="terminology.html#space" id="space_xref27">space characters</a>
</li>
    </ul>
<p><dfn id="character-data" title="character-data">character data</dfn> contains
    <a href="syntax.html#