XML rule based file

Hopefully I can explain this well enough-
I want to build rules into an XML file, fileA, that will be used to verify data in another XML file, fileB. XSD and DTD will not work. The rules will be applied to attribute values as well as element values.

For example,
fileA:
(person firstname=”john” lastname=”doe”)

fileB:
(personrules)
(firstname=”[a-z][A-Z]”)
(personrules)

Then using VB to read in the rules file (fileA) and mark/flag the data file (fileB).

Can this be done?
Thanks, any help is appreciated.