[ Version ( since = "0.15.5" ) ]
public uint group_storage { get; }
Indicates the extent to which contacts' groups can be set and stored.
This property cannot change after the connection has moved to the CONNECTED state. Until then, its value is undefined, and it may change at any time, without notification.
For this property to be valid, you must first call prepare_async with
the feature TP_CONNECTION_FEATURE_CONTACT_GROUPS.