[tei-council] datatypes again: make data.key a URI

[Syd Bauman]

Sebastian is quite right, I meant the general case.

> you can check *this* case, but to be useful you also have to check
> <name key="people.xml#foo">, remember

Even this case could be handled by parsing on "#" and using
document() and id(), I think. But I want to be able to validate at
least
  <name key="http://my.names.org/namesFile.xml#foo">
if not
  <name key="http://my.names.org/namesFile.xml?query=foo">
and all sorts of other URIs as well.