I used to know how to arrange my XSLT modules. Each module had to be self-contained, and any common code imported into all the modules that used it. The reason? Because when you have on-going validation of your XSLT stylesheets, if the module can’t stand alone then you get all sorts of spurious errors. For example, if you define a variable in module A, which includes module B which uses that variable, then although the application as a whole will work fine, when you’re editing module B you’ll get errors because the variable isn’t defined in that module.
That rationale just got blown out of the water.