defined (after all, you cannot wrap something which doesn't exist,
right?).
+We could also get the same outcome by using an attribute trigger. A
+trigger is fired whenever the attribute is I<set>. See
+L<Moose::Manual::Attributes/Triggers> for more information about
+triggers.
+
As with all the other recipes, B<BinaryTree> can be used just like any
other Perl 5 class. A more detailed example of its usage can be found
in F<t/000_recipes/003_recipe.t>.