It need to emulate the behavior of the Struts 1.3.10 HTML tag, in addition to allowing an additional attribute for RDFa. Example: Current: <html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-US"> Should be possible: <html xmlns="http://www.w3.org/1999/xhtml" version="XHTML+RDFa 1.0" xml:lang="en">
Removing from any near-term milestone, this doesn't appear to be necessary at this point in time.