How to create predicate dynamically

Hi

I need to create predicates like the following dynamically:

[@type = 'mc' or @type='ti']

I need the full content of the predicate to be created in a variable
"x", to be inserted in the predicate like:

//qa [$x]

I have tried using saxon:evaluate() but run into problems with
apostrophes. What to do?

Cheers
Jesper Tverskov