After reviewing the current XHTML 2 WD, I have a suggestion. XFrames
are mentioned in the section describing the target attribute Hypertext
Attributes Module
<http://www.w3.org/TR/xhtml2/mod-hyperAttributes.html#adef_hyperAttributes_target >,
but there is no other mention of it. Why shouldn't X(HTML)Frames be
implemented in XHTML 2? The OBJECT tag could possibly be used, but
that requires the specification of dimenstions. Combining several
OBJECTs to create an effect similar to that of a frameset gets fairly
messy. Perhaps an implementation similar to that of the SCRIPT tag
would be a possibility?

<--Scripts-----
<script type="text/javascript" src="example.js">Your user agent does
not support JavaScript or it has been disabled.</script>
------------->

<----XHTMLFrames----
<xframes src="example.xfm" type="application/xhtml+xml">Your user
agent does not support XHTMLFrames.</xframes>
------------->

Just a suggestion.