1. A method at least partially implemented by a computing device for generating extensible metadata, the method comprising: compiling source code to generate an assembly; during compiling operations, emitting metadata and extensible metadata into the assembly, the extensible metadata describing standard and non-standard metadata that represents an extension to standard metadata; and wherein the extensible metadata is configured such that a computer-program application utilizing the extensible metadata can selectively implement behavior associated with the extensible metadata by utilizing a self-describing aspect of the extensible metadata to parse the extensible metadata.