Int 2F Fn 1B  U - Dos 4+ Xma2ems.sys Extension Internal - Get Hidden Fram  [m]

   AH = 1Bh
   AL <> 00h
   DI = hidden physical page number

Return: AX = FFFFh if failed (no such hidden page)
   AX = 0000h if OK, then
       ES = segment of page frame
       DI = physical page number

Notes: this corresponds to the data edited out of the INT 67/AH=58h call
   FASTOPEN makes this call with AL = FFh

See Also: AX=1B00h