Measuring the complexity of XSLT stylesheets

I'm writing a paper where I'm evaluating different XML vocabularies
for expressing the same information, and one of my evaluation criteria
is how easily the resulting XML can be processed with XSLT. At the
moment the paper contains only prose with a subjective appraisal of
the various approaches. This is fine, as far as it goes, but it would
be nice to have something more objective to back it up with. Are there
any established criteria for evaluating the complexity of XSLT
stylesheets?

There are some obvious criteria I could think of, like:

 - size of stylesheet in bytes, lines, and XML elements+attributes,

 - number of elements from the XSLT namespace, and

 - combined length (in characters) of XPath expressions.

I think these criteria would work, but I'm not convinced that they
really capture complexity directly. Can anyone suggest better
alternatives?

-- 
Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
GSM: +47 98 21 55 50                  <URL: http://www.garshol.priv.no >