Rails - Jul 2006 - Cheet shet or overview of visibility between modal, views, and controllers ?

Where is an overview of who can see what and how ?

session[] and params[] seem to be global, but what about instance 
variables of the controller? The views seem to be able to see (and 
modify) them.

components seems to be able to set instance variables that their 
controllers can see; likewise partials can set values that the template 
and layout can see.

I''m getting all the Rails books I can, so a page reference to one of 
them will suffice.

Cheers