Undocumented 
                                                           
This API service or structure is not documented by official
Microsoft sources.  Something may be undocumented for any
of several reasons:

  It is dangerous; you could lose data.
  It may change in future versions of DOS.
  It has no particular value; there are other ways...

In most cases, information contained in TECH Help! has been
gleaned from official Microsoft sources, such as a
Microsoft Knowledge Base on Compuserve or in trusted
publications such as Microsoft Systems Journal.  Some
information was obtained through trial-and-error testing.

In general, it's best to avoid using undocumented features.

Undocumented