XHTML MIME Types note

I see the new version of http://www.w3.org/TR/xhtml-media-types/ has
been published.

Unfortunately, due to being caught up with various minor crises, I
didn't find time to raise formal comments on some of the things in the
latest version before it got out of draft.

So, informally then - could someone explain how the content of iframe
elements is considered different in HTML and XHTML documents? It must be
pretty significant since the content of the element is the only way to
provide alternative content for user agents which don't support or have
frames disabled.

On the same note - how does having JavaScript turned off change the way
the content of the element is evaluated?

-- 
David Dorward                               <http://dorward.me.uk/>