1. Within a system comprising a processor and a memory, a method of processing an Extensible Markup Language (XML) document, the method comprising: loading, via the processor, an execution plan into a virtual machine, wherein the execution plan represents an XML schema and specifies a hierarchy of XML components, and wherein the virtual machine comprises a plurality of dedicated XML processing functions specifically corresponding to the XML components specified by the XML schema; selectively invoking, via the processor, the XML processing functions available within the virtual machine according to the execution plan, wherein the XML processing functions operate upon an XML document; and outputting, via the processor, an indication of whether the XML document is valid according to the XML processing functions.