just like Perl's core C<map> function. This method requires a subroutine which
implements the transformation.
-Note that if you add or subtract values within the supplied coderef, the
-values are I<not> saved back to the attribute. You need to use the attribute
-writer wrapped around the map call for that.
-
my @mod_options = $stuff->map_options( sub { $_ . "-tag" } );
print "@mod_options\n"; # prints "foo-tag bar-tag baz-tag boo-tag"