What is a "valid" document for doc.attachvcard?

Hello,

i wanna use notesdocument.attachvcard in my own application. Designer help says: “If documents are not Contact documents, the documents will not be attached, and the error “Attach of VCard failed” will be thrown.”

I can’t find information, which items must be set to become a valid “contact” document…

Does anybody know?

Greetz Oliver