Namespaces and xpaths

All,

I have a question about namespaces and xpath expressions. There are a
few standard xpath functions in XACML 2.0 in section A.3.15. These
functions take strings as parameters, where the strings are to be
interpreted as xpath expressions.

How is resolving of namespace prefixes in these strings/expressions
done? The specification doesn't say anything about this. (Or I didn't
find it.)

Is the xpath function going to trace back its input to the xml document
from where the string came from? This doesn't seem possible in general.
Or does it find the