Devel::callchecker makes some new features of the perl 5.14.0 c api available to xs modules running on older versions of perl. the features are centred around the function cv_set_call_checker, which allows xs code to attach a magical annotation to a perl subroutine, resulting in resolvable calls to that subroutine being mutated at compile time by arbitrary c code. this module makes cv_set_call_checker and several supporting functions available. (it is possible to achieve the effect of cv_set_call_checker from xs code on much earlier perl versions, but it is painful to achieve without the centralised facility.)