If the following webpage is correct about the
definition of a comment, HTMLParser.HTMLParser reports
valid (albiet strange) comments as being erroenous:

http://www.htmlhelp.com/reference/wilbur/misc/comment.html

This site gives '<!>' as an example of a valid html
comment. See attachment for what happens at the
console. A similar thing happens with other
(pathalogical) form of comments.

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Sorry, I'm unfamiliar with the bug reporting system and my
attachment doesn't seem to have attached.

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I recommend this as a wontfix.  

As the page itself notes, browsers generally got this 
wrong, and existing webpages rely on this buggy behavior.  
Even today, Opera is going back and forth on how right they 
can afford to be without breaking too many pages.

The suggestion at the bottom of the page notes that if you 
keep your comments sane, you won't have problems on your 
own pages.  Realistically, anything not following that rule 
(no embedded -- or >) is effectively buggy, and HTMLParser 
can only guess at the real intention.

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Updated markupbase to cope with "<!>" in rev. 42938.