rminology.html#must-requirement" id="must-requirement_xref17">must</a>
      be serialized completely within the first
      512 bytes of the document.</li>
    </ul>
<p>If the document does not start with a
    U+FEFF BYTE ORDER MARK (BOM) character, and if its
    encoding is not explicitly given by a
    <code>Content-Type</code> HTTP header, then the character
    encoding used
    <a href="terminology.html#must-requirement" id="must-requirement_xref18">must</a>
    be an
    <a href="syntax.html#ascii-