Read-only. The universal ID of a document's parent, if the document is a response. Returns an empty string ("") if a document doesn't have a parent.
String
To get: parentUnid$ = notesDocument .ParentDocumentUNID
When used in conjunction with the GetDocumentByUNID method in NotesDatabase, the ParentDocumentUNID property allows you to find the parent document for any document.
For more information on universal IDs, see the UniversalID property.
ParentDocumentUNID property in Java™ Document class
@InheritedDocumentUniqueID function in formula language