INT 15 - TopView - "OSTACK" - SWITCH TO TASK'S INTERNAL STACK
AX = 101Ah
Return: stack switched
Notes:  this call may not be nested; a second call must be preceded by a call
to "USTACK" (AX=1025h)
while TopView requires many API calls to be executed while on the
task's internal stack, DESQview allows those calls to be executed
regardless of the current stack

See also: 151025

15101A - TopView - "OSTACK" - SWITCH TO TASK'S INTERNAL STACK