1. At a computer system including one or more processors and system memory, a method for determining how to process markup codes within programming language source code when programming language source code is compiled, the method comprising: an act of accessing one or more portions of programming language source code, the one or more portions of programming language source code including some markup codes; an act of declaring further code that defines relationships between specified code constructs and the included markup codes, the specified code constructs being code constructs that are to be referenced or executed when the included markup codes are encountered during compilation; and an act of the processor compiling the one or more portions of source code along with the declared further code, including during compilation: an act of encountering a specified markup code within the portion of source code; an act of identifying a relationship between the specified markup code and a specified code construct, from within the declared further code, that is to be referenced or executed when the specified markup code is encountered during compilation; and an act of calling or emitting a call to the specified code construct.