[New in v9.0]
The ValidateXMLDocument (XMLOK) functions will now check against the huge catCFDI.xsd and other XSD catalogs.
There is a small chance (less than 1 in 100) of a false positive, where an incorrect attribute value is passed as valid.
However, if an attribute value is rejected as not in the catalog then it is definitely an error.
Formerly, only general checks on the pattern of the value were made.