title: Can a valid HTML comment tag contain an attribute-like syntax?
body: <p>I'm trying to discern if the attribute syntax characters (quoted key-value pairs) are valid within HTML comments:</p>
     
  <p>I can't tell if this is valid.  I looked at:</p>
  <ul>
  <li><a href="http://dev.w3.org/html5/spec-author-view" rel="nofollow noreferrer">http://dev.w3.org/html5/spec-author-view</a></li>
  <li><a href="http://www.w3.org/TR/html-markup/syntax.html" rel="nofollow noreferrer">http://www.w3.org/TR/html-markup/syntax.html</a></li>
  </ul>
  <p>It appears that they probably are—except for a few references to &quot;control characters&quot;.  I can't find a definition for control characters in the specification.</p>
  <p>The specification only requires:</p>
  <ul>
  <li>comment open &quot;&lt;!--&quot;</li>
  <li>text</li>
  <li>comment close &quot;--&gt;&quot;</li>
  </ul>
  <p>Most browsers and parsers support having a quoted key-value pair in a comment.  I've ran into a few issues with various open source libraries that can sometimes choke.</p>