If your xml is valid and compliant, the first part of the pointer should be invariant...
hence:

grep &/or a regex will work ... but parsing html or xml with a regex is not usually a good idea because a small departure from compliant xml or html is apt to make your effort fail in any number of unpleasant manners.

A parser is likely to do a better job, at the price of a brief learning curve on use of the module your select. XML::Twig is often suggested among the several hundred XML modules available from CPAN (or, if on windows w/ActiveState), via PPM.

(And if your goal is checking the style sheet, note the XSL::... modules.)