+ Moreover, when you pass "op_info => $num" to "wizard", the last
+ element of @_ will be the current op name if "$num ==
+ VMG_OP_INFO_NAME" and a "B::OP" object representing the current op
+ if "$num == VMG_OP_INFO_OBJECT". Both have a performance hit, but
+ just getting the name is lighter than getting the op object.
+
+ Other arguments are specific to the magic hooked :
+
+ * "len"
+
+ When the variable is an array or a scalar, $_[2] contains
+ the non-magical length. The callback can return the new
+ scalar or array length to use, or "undef" to default to the
+ normal length.
+
+ * "copy"
+
+ $_[2] is a either a copy or an alias of the current key,
+ which means that it is useless to try to change or cast
+ magic on it. $_[3] is an alias to the current element (i.e.
+ the value).
+
+ * "fetch", "store", "exists" and "delete"
+
+ $_[2] is an alias to the current key. Nothing prevents you
+ from changing it, but be aware that there lurk dangerous
+ side effects. For example, it may rightfully be readonly if
+ the key was a bareword. You can get a copy instead by
+ passing "copy_key => 1" to "wizard", which allows you to
+ safely assign to $_[2] in order to e.g. redirect the action
+ to another key. This however has a little performance
+ drawback because of the copy.
+
+ 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 "len" callback currently holds a meaning.
+
+ 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.
+
+ Note that "free" callbacks are *never* called during global destruction,
+ as there's no way to ensure that the wizard and the "free" callback
+ weren't destroyed before the variable.
+
+ Here's a simple usage example :
+
+ # A simple scalar tracer
+ my $wiz = wizard get => sub { print STDERR "got ${$_[0]}\n" },
+ set => sub { print STDERR "set to ${$_[0]}\n" },
+ free => sub { print STDERR "${$_[0]} was deleted\n" }
+
+ "cast"
+ cast [$@%&*]var, $wiz, ...
+
+ This function associates $wiz magic to the variable supplied, without
+ overwriting any other kind of magic. It returns true on success or when
+ $wiz magic is already present, and croaks on error. All extra arguments
+ specified after $wiz are passed to the private data constructor in @_[1
+ .. @_-1]. If the variable isn't a hash, any "uvar" callback of the
+ wizard is safely ignored.
+
+ # Casts $wiz onto $x, and pass '1' to the data constructor.
+ my $x;
+ cast $x, $wiz, 1;
+
+ The "var" argument can be an array or hash value. Magic for those
+ behaves like for any other scalar, except that it is dispelled when the
+ entry is deleted from the container. For example, if you want to call
+ "POSIX::tzset" each time the 'TZ' environment variable is changed in
+ %ENV, you can use :