A compiled module will need to be defined as something more closed. It
may be a collection of many compiled stylesheets. What is important is
its property that it doesn't use/know about global objects that exist
outside this module (such as global variables, keys, etc). The only
way to pass information to this module is by using parameters.

And this affects the decision whether to add an attribute to xsl:include or
to use a new top-level element. If an attribute is added to xsl:include, the
semantics must be identical to xsl:include - loading the precompiled code is
then merely an optimization.

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