What's the basic concept behind rails' act_as?

Question

I can't seem to find the answer to this,
I somewhat see what it does through implementation, but don't grok the sense of it..

Answer 1

Yehuda Katz has a nice explanation of the acts_as plugin pattern and why it's usually implemented in a needlessly complicated way.

Answer 2

This article explains the acts_as plugin architecture using the acts_as_state_machine plugin as an example.