I'd like to understand more about the standard exception
classes that are defined for Ruby.

I found a hierarchy diagram in the pickaxe book, showing
which inherit from which others, but that doesn't really explain
under what circumstances each type is normally raised.

Icould  grep the Ruby source code, but before I do that, I thought
I'd ask whether there's some documentation somewhere that
would save me delving in quite that deep.

Any suggestions?