According to the yellow paper, one of the Execution Environment variables is:
Iw, the permission to make modifications to the state.
I can't find further information about it, for example how it's set and what values it can get (I guess 1 or 0)
Also I'd like to make sure that the variable
Ie, the depth of the present message-call or contract-creation (i.e. the number of CALLs or CREATEs being executed at present).
is only decremented by one for each CALL and CREATE opcodes, but never for a DELEGATECALL or CALLCODE