1. A system comprising: one or more processors; and a memory storing program instructions, wherein the program instructions are executable by the at least one of the one or more processors to implement: a script processing module configured to: process a plurality of instructions in a script, wherein the instructions reference one or more classes defined by respective markup language structures in a markup language schema that includes markup language structures for a plurality of classes; and determine that a current instruction being processed indicates that an instance of one of the one or more classes that is referenced by the current instruction is to be created; and a class object module configured to, in response to said determining: obtain class metadata for the class referenced by the instruction; generate an instance of the class as a class object according to the class metadata for the class; and load the class object into a runtime environment.