> It all works fine except for one thing: where I have a 
> template which matches one of the elements from the main 
> content file, e.g. "image", I can't seem to access the 
> hierarchy of the map file in XPath expressions:

As a general rule, if you're processing more than one document, then it's
best to avoid path expressions beginning with "/", as you and your readers
will both get confused about which document "/" is referring to (the answer
is: the root of the document containing the context node). Instead, bind
variables to the root nodes of both documents, and use path expressions that
start with a variable reference.

Michael Kay
http://www.saxonica.com/