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 class object module configured to load classes in a runtime environment; and a script processing module configured to: process instructions from a script comprising a plurality of instructions, wherein one or more of the plurality of 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; determine, during said processing instructions from the script, that a current one of the plurality of instructions 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 generate a request for the class referenced by the current instruction in response to said determining; wherein the class object module is configured to, in response to said request: obtain class metadata for the class referenced by the current 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 the runtime environment; wherein the script processing module is configured to continue said processing instructions from the script subsequent to said generating the request.