1. A method performed by a managed execution environment operating on a computer comprising a processor and associated memory structures, the managed execution environment for executing assemblies compiled to run in the managed execution environment, every such assembly including bytecode and metadata produced by a compiler for the managed execution environment, the metadata of each assembly received by the runtime execution environment describing data types referenced in the compiled bytecode of the assembly, the runtime execution environment having a built-in ability to interpret the structure of any metadata that is structured in conformance with a standard metadata schema of the runtime execution environment, the built-in ability allowing the runtime execution environment to interpret the structure of any assembly's metadata when such assembly does not include the standard metadata schema, the standard metadata schema defining the structure that metadata must have to be interpreted by the built-in ability of the runtime execution environment, the method performed by the runtime execution environment comprising: receiving one of the assemblies compiled to execute in the runtime execution environment, where the metadata in the assembly is not structured in accordance with the standard metadata schema of the managed execution environment; analyzing the received assembly to determine that the metadata of the assembly is not structured in accordance with the standard metadata schema; in response to determining that the metadata of the assembly is not structured in accordance with the standard metadata schema, accessing meta-meta-data included with the assembly, the meta-meta-data extending and/or modifying the structure defined by the standard schema and using the meta-meta-data to interpret the structure of the metadata included with the assembly to obtain from the metadata information about data types referenced in the bytecode; executing the assembly in accordance with the data type information.