Strange source code of PGP for Notes

Have you ever taken a look at the source code of PGP for Notes? There are some codes I can't understand. Could you please explain them?
@DbCommand( "PGP"; vn_hNOTE; vt_ITMNM_RTF)
What is "PGP"? A database name or a DLL name?
It is the name of a DLL -- we would attempt to do a load library on it. This DLL would implement certain DB extensions.

This was first published in August 2003