I don't know when Lotus added this property to Notes, but I first discovered it in 5.09 and verified it was still in R6 PR1. It seems to flag whether the user has changed any item in an open document since the last time it was saved. It's not described in Designer Help for either version, so use it with caution.
Defined In: NotesUIDocument.
Return Value: Integer; Returns True if user has entered data into any field on a new document, or modified any field on an existing document since it last was saved, False if no fields have been modified.