see ยง3.1.1.3 of rfc 4287. The datatype of xhtml text elements.
skos:editorialNote
Note that there is a tricky question concerning the xml div element. The xml:lang and xml:base elements are not in fact part of xhtml and it has been argued on the atom mailing list (28 June 2006) that the div is *not* part of the xhtml. We could have this be a special literal with the div, or we could remove the div and push the xml:lang and xml:base down (this would work only if there is one element beneath I suppose) or we would have to use the awol:lang and :base relations on the :Content object.