-Code references to corresponding magic callbacks. You don't have to specify all of them : the magic associated with undefined entries simply won't be hooked. In those callbacks, C<$_[0]> is always a reference to the magic object and C<$_[1]> is always the private data (or C<undef> when no private data constructor was supplied). In the special case of C<len> magic and when the variable is an array, C<$_[2]> contains its normal length. C<$_[2]> is the current key in C<copy>, C<fetch>, C<store>, C<exists> and C<delete> callbacks, although for C<copy> it may just be a copy of the actual key so it's useless to (for example) cast magic on it. C<copy> magic also receives the current element (i.e. the value) in C<$_[3]>.
+Code references to corresponding magic callbacks.
+You don't have to specify all of them : the magic associated with undefined entries simply won't be hooked.
+In those callbacks, C<$_[0]> is always a reference to the magic object and C<$_[1]> is always the private data (or C<undef> when no private data constructor was supplied).
+In the special case of C<len> magic and when the variable is an array, C<$_[2]> contains its normal length.
+C<$_[2]> is the current key in C<copy>, C<fetch>, C<store>, C<exists> and C<delete> callbacks, although for C<copy> it may just be a copy of the actual key so it's useless to (for example) cast magic on it.
+C<copy> magic also receives the current element (i.e. the value) in C<$_[3]>.
+
+All the callbacks are expected to return an integer, which is passed straight to the perl magic API.
+However, only the return value of the C<len> callback currently holds a meaning.