Regex for XPath schema type?

Heyas,

I'm building a schema, which is supposed to contain some XPaths as data
types (that is, certain attributes in instance documents based on this
schema are expected to contain XPaths, which point into yet-another
document ...).

So, I would like to have a data type for XPath.  I started down the
path of writing the <pattern> ... and then wondered ... has anyone
already done this?

Is it possible to do, in fact, given that at some points an XPath can
contain almost anything?

I know that given time, I can turn the BNF in the spec into a regex
(using XSDL pattern facet notation), but I'm hoping that someone may
already have done so.  Web searches haven't turned up anything
promising as yet.

Amy!
-- 
Amelia A. Lewis                    
There's someone in my head, but it's not me.
		-- Pink Floyd