Int 21 Fn 55  - Dos 2+ Internal - Create Child Psp                         [D]

   AH = 55h
   DX = segment at which to create new PSP
   SI = (DOS 3.0+) value to place in memory size field at DX:[0002h]

Return: AL destroyed

Notes: creates a "child" PSP rather than making an exact copy of the current
     PSP; the new PSP's parent pointer is set to the current PSP and the
     reference count for each inherited file is incremented
   (DOS 2.0+) sets current PSP to DX
   (DOS 3.0+) marks "no inherit" file handles as closed in child PSP
   this function is implemented using the same code as AH=26h, so unlike
     other DOS 2+ functions, it does not return status in CF, instead
     returning status in AL as DOS 1.x functions do (but it never puts an
     explicit return value in AL)

See Also: AH=26h,AH=50h