- Each callback can be specified as a code or a string reference, in which
- case the function denoted by the string will be used as the callback.
+ Each callback can be specified as :
+
+ * a code reference, which will be called as a subroutine.
+
+ * a string reference, where the string denotes which subroutine is to
+ be called when magic is triggered. If the subroutine name is not
+ fully qualified, then the current package at the time the magic is
+ invoked will be used instead.
+
+ * a reference to "undef", in which case a no-op magic callback is
+ installed instead of the default one. This may especially be helpful
+ for 'local' magic, where an empty callback prevents magic from being
+ copied during localization.