Synopsys:
strref
Given a string and an unsigned long at the top of the stack, push an unsigned integer with the code of the character that occupies that position in the string, on the stack.
The index is zero-based. If it is less than 0 or exceeds the length of the string, then PVM_E_OUT_OF_BOUNDS is raised.
Stack: ( STR ULONG -- STR ULONG UINT )
Exceptions: PVM_E_OUT_OF_BOUNDS