This is best described by showing the mark-up validator's error message, one of which can be seen here .

The iframe, which may be unavoidable is not valid XHTML Strict, and there are a few other errors which are not valid whatsoever.

Comments

robloach’s picture

robloach
he/him
commented
Status: Active » Fixed

I posted a note on the reCAPTCHA discussion group. Hopefully they will fix the issue as there's nothing we can do about it in the Drupal reCAPTCHA module.

tc1415’s picture

tc1415 commented

I thought that might be the case, thanks for the prompt response.

robloach’s picture

robloach
he/him
commented
Status: Fixed » Closed (won't fix)

They followed up:

It actually turns out the problems are deeper than this. We use
document.write, which is not valid with XHTML. Very few AJAX apis (Google
Maps, Adsense, many counters, etc) are actually XHTML compliant, even though
the markup may appear to be valid XML.

Very unfortunate, damn Microsoft, eh? ;-)

tc1415’s picture

tc1415 commented

Yes, true. Would be nice if we could at least have valid markup I suppose - but its moot if it doesn't follow the spec in other ways.