So, this is a general design question for XML document definitions
rather than a specific question about XHTML.

In XML document definition design, I usually promote the viewpoint
that different published versions of a document definition should have
different namespace identifiers, especially if there are non-trivial
differences to the definitions. The loosely defined "space" of "names"
has changed; for compatibility, different identifiers should be used
for each space.

The counterargument to this principle, of course, is XHTML 1.0 and
1.1. These are two different document definitions -- elements allowed
in 1.0 aren't allowed in 1.1 -- yet they have the same XML namespace.

I can't find a good explanation for why this is. This seems to violate
the W3C namespace policy template stated here:

     http://www.w3.org/1999/10/nsuri 

...in particular, borrowed from the template there,

      "This namespace name (URI) will only be used to refer to this
      version of this specification: different URIs will be used for
      any and all new versions of the specification"

I can't seem to find a contradictory namespace policy for the XHTML
namespace URI. Is my principle stated above -- different group of
names, different namespace -- deeply flawed? Or was some kind of
exception made for XHTML? Am I missing something obvious?

Much thanks for attention to an off-topic question,

~ESP

-- 
Evan Prodromou
evan@prodromou.san-francisco.ca.us