A reference to a license is acceptable if and only if the license being referenced recognizes them. Some licenses (like GPL) do recognize certain types of refe

A reference to a license is acceptable if and only if the license being referenced recognizes them. Some licenses (like GPL) do recognize certain types of references while others (like MIT) do not. If you want a C analogy, saying "LICENSE: GPL" or "LICENSE: MIT" is like dealing with a void *.