As any compiler, PostSharp can emit messages, warnings, and errors, commonly referred to as message. Custom code running at build time (typically the implementation of CompileTimeValidate or of a custom constraint) can use PostSharp messaging facility to emit their own messages.
In this section:
Tip
PostSharp 2.1 contains an experimental feature that adds file and line information to errors and warnings. The feature requires Visual Studio. In must be enabled manually in the PostSharp tab of Visual Studio options.