"Dark Lego, show me the forbidden connection techniques":
http://bramlambrecht.com/tmp/jamieberard-brickstress-bf06.pdf
a leaked PDF of a Lego internal corporate document describing "illegal" connections that must not be used in official kit-building instructions
Much has been written on the analogy between lego connections and programming language syntax; that would make this illegal connection PDF the equivalent of, like, undocumented compiler features or something.