=over =item prototype FUNCTION Returns the prototype of a function as a string (or C<undef> if the function has no prototype). FUNCTION is a reference to, or the name of, the function whose prototype you want to retrieve. If FUNCTION is a string starting with C<CORE::>, the rest is taken as a name for Perl builtin. If the builtin is not I<overridable> (such as C<qw//>) or its arguments cannot be expressed by a prototype (such as C<system()>) returns C<undef> because the builtin does not really behave like a Perl function. Otherwise, the string describing the equivalent prototype is returned. =back