Open a new IO space. The handler string and a set of flags are passed on the stack. The descriptor of the opened IOS is pushed to the stack as a signed integer.
If there is no other IO space opened when this instruction is executed, then the just opened space becomes the current IO space.
If it is not possible to open the IO space according to the provided flags, the PVM_E_IOFLAGS exception is raised. If there is any other error performing the operation, PVM_E_IO is raised.
( STR ULONG -- INT )