[KevinH]

Okay I checked the python3lib sanitycheck.py code and it will treat "<<p>" as a spurious text "<" followed by a tag. And it will treat "</p>>" or "<p>>" as a tag followed by a spurious text ">".

I could detect both cases by verifying that the text returned from parsing does not contains an illegal > or < char when not a child of a CDATA tag.

So making sanity check detect these cases is doable. I will look into doing that.

FWIW, HTML5 parsing rules only require xml escaping a ">" in text if it would be considered to result in ambiguous parsing. Whereas the "<" character should always be xml escaped when used in attribute values and text. Under XHTML, both characters should always be xml escaped when used inside attribute values and text fields.