XPLC is a component framework, similar to what MicroSoft has done with ComponentObjectModel or TheMozillaProject has done with XpCom, but with slightly differing goals (that could or could not be related to ExtremeProgramming).
Here's an article about the design of XPLC: http://advogato.org/article/222.html. -- PierrePhaneuf
Well, there is no sufficient explanation and documentation of XPLC so I will ignore it.