This property identifies the instance of E39 Actor that becomes member of an instance of E74 Group in an instance of E85 Joining.
Joining events allow for describing people becoming members of a group with the more detailed path E74 Group, P144i gained member by, E85 Joining, P143 joined, E39 Actor, compared to the shortcut offered by P107 has current or former member (is current or former member of).