the contact responsible for the change, or 0 if no contact was responsible
A specific reason for the change, which may be a D-Bus error in the Telepathy namespace, a D-Bus error in any other namespace (for implementation-specific errors), or the empty string to indicate that the state change was not an error
A developer readable debug message giving the reason for the state change.
the reason for the change. If
#TP_CALL_STATE_CHANGE_REASON_USER_REQUESTED then the actor member will
dictate whether it was the local user or a remote contact responsible
Data structure representing the reason for a call state change.