Set the call stack index to the given value. 0 is the normal value indicating the current top of the call stack, i.e. what is executing. 1 is the function that called it, etc. If it is out of range, the result will be a DENIED, else it will be:
STACK SET TO index
Once the call stack index is changed, all of the reporting functions are going to return values relative to that index. For instance, REPORT gives the file/line number of the function in that index, GET LOCAL refers to the local variables of that function, and so forth.