We all like attributes - don't we?
Well, I really like attributes in .NET. And this idea is just so plain cool and powerful that Microsoft has a patent on it.
Extending program languages with source-program attribute tags
Attribute tags embedded in the statements of a source program system extend a programming language. A compiler for the program includes an interface to detect the attribute tags and to call one of a number of attribute-provider programs external to the compiler. The provider programs modify the operation of the compiler, for example by injecting additional statements or other code into the program at one or more predetermined points remote from the attribute tag. The compiler interface lists the names of the attributes and locations of their associated provider programs.