[Radiant] Custom Tags and Code reuse

[Michael Jones]

> The tags that are rendered in the 'tag.expand' call set values in the hash.
> Look at their definitions and you'll see it.

I must be missing it, I don't see an expand method anywhere other than here:
http://radius.rubyforge.org/classes/Radius/TagBinding.html#M000011

And with that I don't see how the 'hash' is passed to that method
inorder to set values in it?