Casting rules

[JG]

Where can I find rules about casting. e.g. I assume casting away 
immutable is undefined behavior (or implementation defined 
behavior). What about casting to immutable (I would expect at 
most it only to be allowed if your type has no references e.g. 
ints okay but int[] not etc.) Casting const away (probably not 
allowed)? Casting to const (probably allowed).

Anyhow guessing aside where can I find the rules?