Suggestion for very slight improvement to 1.1 draft

I think the changes look good and the goal is admirable.

One thing that the 1.0 draft didn't say clearly enough is
that the empty string, while it's a valid URI reference,
can never be a namespace name.  It's implicit in the 
spec if you read it carefully enough, but I've had to
demonstrate & explain this enough times that it's probably
worth stating explicitly simply as a matter of spec 
usability.

Note that this is actually a useful fact, and 
denoting "no namespace" as the empty string
rather than null allows simplification of code
in languages like Java.  -Tim