One other slight difference (again due to the change in bitness of the
  internal workings of PM) is WinTrackRect.

  If you install a hook function in WinTrackRect in OS/2 version 2.xx,
  you have to call Win16TrackRect and use a 16-bit callback function for
  your hook if you want to be able to (say) display the co-ordinates of
  the rectangle as the user is moving it around the screen.

  This is because the 32-bit PM API on that version of OS/2 thunks the
  TRACKINFO structure to its 16-bit equivalent internally and uses that
  internal structure during tracking. Thus the RECTL structures in the
  32-bit structure are not updated as the rectangle tracks, and any
  32-bit hook doesn't actually display the correct co-ordinates.

  However, on OS/2 WARP Three, that part of PM is now 32-bit, and it is
  now the 16-bit function that thunks to 32-bit internally, rather than
  the other way around.  So it is then hook code that uses the 16-bit
  TRACKINFO structure that doesn't see the rectangle boundaries as they
  are updated.

  > JdeBP <
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