John Jacks wrote:
> Since this is all 'in a string value',

Without the surrounding comment markers, Mike's suggested syntax
wouldn't be legal xpath syntax so in particular not a string.

> XPath processors that don't understand
> it would treat it as a string surely?

No,

 xmlns=http://default/uri xmlns:p=http://other/uri  xpath-expression

would be an Xpath  parse error (at the first colon)


> Why mess with comments?
>  The James Clark notation has been around for a while and regularly
> re-used?

That though doesn't bind prefixes, it just does away with the need for
prefixes altogether, so instead of

(:# xmlns:p=http://other/uri #:) /p:foo/p:bar[2]

you'd write

/{http://other/uri}foo/{http://other/uri}bar[2]

which is workable, but a bit long winded, especially in attribute value
templates, where { already has another meaning, and so would need to be
quoted.

David