CALL BACKs
     ----------

QLIB provides these servies for using callbacks:

alloc_callback(dword your_proc,dword call_back_struct,byte typ);
  - this is used to alloc the callback
  - your_proc should be the offset of your proc to call
  - call_back_struct must be the offset of a callstruct<> that you must
    have in your data segment (although DOS32 does not require this, DOS/4GW
    and PMODE/W do so you must use one at all times)
  - typ is the type of callback you wish to get:
    CB_RETF = retf stack frame 
    CB_IRET = iret stack frame
  - ax:dx is returned which is the (CS:IP) of the real mode callback

_iret(dword call_back_struct);
  - this must be called at the end of your proc if you are using a
    iret stack frame
  - this function does not return (it ends your proc and passes control
    back to real mode)

_retf(dword call_back_struct);
  - this must be called at the end of your proc if you are using a
    retf stack frame
  - this function does not return (it ends your proc and passes control
    back to real mode)

free_callback(_seg:word,_off:word)
  - this frees a callback (_seg and _off are values you received from
    alloc_callback() )

If you use the above then your code will always work.  If you know you are
using a specfic DOS extender and will to use it's function directly you may,
but make sure to indicate this in your source code if you plan on releasing
the source.