A programmatic value that identifies the type of external ID.
It is mutually exclusive with label. Examples are gdata_gcontact_external_id_network or gdata_gcontact_external_id_account .
For more information, see the <ulink type="http" url="http://code.google.com/apis/contacts/docs/3.0/reference.html#gcExternalId"> gContact specification</ulink>.