A value that uniquely identifies the vCard.
Namespace: vCardsAssembly: ICalVCard (in ICalVCard.dll) Version: 1.0.0.0 (1.0.0.0)
Syntax
Remarks
This value is optional. The string must be any string
that can be used to uniquely identify the vCard. The
usage of the field is determined by the software. Typical
possibilities for a unique string include a URL, a GUID,
or an LDAP directory path. However, there is no particular
standard dictated by the vCard specification.