[xml] double namespace problem

["Marek Elsner" <marek icom pl>]

Hello,
I know that this problem is very easy to solve, but I have no idea how to do
it.
Sorry but I am starting with XPath. :-)
I have got xml file with two namespaces, one inside another.
As I know when I have one namespace, I can register it, and after that
query as "//namespac_name:node"
but how to do queries, when I have another namespace in namespace_name, and
I want to find a node inside two namespaces...?

thanks for help

Marek Elsner