1. A platform independent XML virtual machine that accepts application code written in an XML programming language as input and implements a method that causes the application code to be executed on a computing device, the method comprising: defining a set of runtime objects for executing an application including an instance object configured to couple operational meaning to the execution of the application's process code; providing low-level constructs (“operation handlers”) that execute operations defined in the application's process code; and implementing logic that allows stateless process objects to provide operation handlers with an instance object that accounts for changes in the application's runtime state when executing the application's process code.