I thought HTLM4 conformance was documented somewhere, but I could be wrong.

HTML5, from what I understand (I haven't read the spec), is explicitly or implicitly following "what browsers really do" exactly because nobody conformed to HTML4, so arguing that "a later spec changed the rules" isn't really relevant in this case :)

We made the change the way we did (strict option) out of backward compatibility concerns, so I still think this topic needs to be discussed on python-dev.  I think the argument that python should handle what most browsers handle is a strong one (I myself would have been in favor of just making this stuff work, absent backward compatibility concerns).  The question in my mind is what's the best way to get there from here?