        <li>zero or more
            <a href="terminology.html#space" id="space_xref20">space characters</a>
</li>
            <li>an
            <a href="syntax.html#syntax-attribute-value" id="syntax-attribute-value_xref2">attribute value</a>
</li>
          </ol>
<p>In addition to the general requirements given above for
          attribute values, an unquoted attribute value has the
          following restrictions:</p>
          <ul>
<li>
<a href="terminology.html#must-requirement" id="must-requirement