Hi,

I think that document fragments, whether they be structurally or 
conceptually coherent, need to be permitted formal expression in XHTML. 
The simplest illustration of this may be xhtml microformats.

Bracing microformats (and other fragments) using globally unique 
identifiers would permit machine isolation and analysis, cross 
referencing, consensus, scriptability, coalescence, and the association 
of folksonomies with high resolution.

Please consider an attribute capable of accepting an arbitrary 'unique 
concept / null concept' identifier.

<div identity="3C05DC85-DC34-4546-9210-02EC43188367" id="MyCard" 
class="hCard">Content</div>

In this case 3C05DC85-DC34-4546-9210-02EC43188367 may achieve consensus 
as an hCard microformat reference.  Can you speculate how this will 
scale? I thought it good enough to share.