Int 15 Fn 1018  - Topview - "locate" - Find Window At A Given Screen Loca  [Q]

   AX = 1018h
   BH = column
   BL = row
   ES = segment of object handle for window below which to search
        0000h = start search with topmost window

Return: ES = segment of object handle for window which is visible at the
          indicated position, or covered by indicated window
      = 0000h no window

See Also: AX=1023h,AX=1024h