Excerpts from John Carter's mail of 22 Sep 2005 (CDT):
> Ok, so I'm documenting a Mixin.
> 
> Can anyone think of a more sane word / phrase than "The class that it
> is mixed in to"?

Mixee.

> In particular has anyone devised a standard way of documenting /
> enforcing the signature that "the class that it is mixed in to" must
> conform to.

I suspect most people treat this as falling under the duck typing
principle: just call the method, and if the object doesn't respond, an
error will be raised.

You could call #respond_to? from within append_features, and that would
work for very simple cases. But all you'd be doing is moving a run-time
exception to an earlier part of the program execution. Really, your
best bet is to a) document your module well then b) ignore the problem.

-- 
William <wmorgan-ruby-talk / masanjin.net>