This sentence feels a bit incomplete, particularly since I don't think it'll render as a link.  Plus the file is `message_expectations/expect_any_instance_of`.

Maybe it should say this?

> Note: you can use `expect_any_instance_of` when you don't have a reference to the object that receives a message in your test.  For more information, see the `message_expectations/expect_any_instance_of` feature.

Among other things, I prefer not to say "you should use `expect_any_instance_of`" -- I'd actually recommend folks avoid it, but that's a different story (it's largely there to assist in getting legacy code under test).

Is there a place we should put a similar note about `allow_any_instance_of`?