A regex-based "parser", on the other [email protected] indeed, if having to know all the gotchas and workarounds to get an 80% solution that fails the rest of the time "works for you", I can't stop you.
Meanwhile, I'm over on my side of the fence using parsers that work on 100% of syntactically valid XML.
HTML and regex go together like love, marriage, and ritual infanticide. The force of regex and HTML together in the same conceptual space will destroy your mind like so much watery putty.
If you parse HTML with regex you are giving in to Them and their blasphemous ways which doom us all to inhuman toil for the One whose Name cannot be expressed in the Basic Multilingual Plane, he comes.
Maybe if you give examples of the "(X)HTML syntax errors implemented in real world user agents" you're referring to, I'll understand what you're getting at [email protected] Mihalcin is exactly right.