1. A computer readable medium for use in validating an extensible Markup Language (XML) message in a particular wire format, said computer readable medium containing computer-executable instructions which, when performed by a processor in a computing device, cause the computing device to: from a custom XML schema based message model having at least one wire format specific rendering option associated with an XML entity representing at least a portion of said message, generate an XML schema fragment for use in validating said XML message at a node which lacks said custom XML schema based message model, said XML schema fragment conforming to said particular wire format.