> Given two stylesheets with the same namespaces defined at the 
> top where one imports the other - what happens when the 
> module is compiled?

Entirely implementation-defined.

In Saxon, any instruction/expression that needs access to the namespace
context at run-time will (at compile time) make a copy of the namespace
context and save it on the expression tree. It's true that there is
therefore a slight overhead in having unused namespaces present in the
stylesheet - but I doubt it is measurable.

I can't quite see how import comes into this, however.

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