Empty span/div tags in RDFa pages

Hi,

According to the examples of http://www.w3.org/TR/rdfa-syntax/#sec_6.1.1.5.1.
it is allowed to use the shorthand notation for empty span/div tags in
RDFa+XHTML:
  <div rel="dbp:birthPlace" resource="http://dbpedia.org/resource/Germany"
/>

However, according to XHTML 1.0 specs [1]:
"Given an empty instance of an element whose content model is not EMPTY (for
example, an empty title or paragraph) do not use the minimized form (e.g.
use <p> </p> and not <p />)."

There are only 10 EMPTY tags in HTML 1.0, and neither div nor span is part
of these. I looked in XHTML 1.1 and didn't find anything. The RDFa DTD [2]
does not declare new EMPTY tags either. Can someone point me to some specs
or a DTD which explains why the empty tag notation is allowed in RDFa?

On a side note, firebug does not render these well, and wraps the empty span
around the next sibling tag [3]. That might be a firebug bug...

Stephane.

[1] http://www.w3.org/TR/xhtml1/#C_3
[2] http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd
[3] http://skitch.com/scor/nrpat/empty-tags-firebug-bug