An agent joins an event/group with participants/friends at a location.\n\nRelated actions:\n\n* [[RegisterAction]]: Unlike RegisterAction, JoinAction refers to joining a group/team of people.\n* [[SubscribeAction]]: Unlike SubscribeAction, JoinAction does not imply that you'll be receiving updates.\n* [[FollowAction]]: Unlike FollowAction, JoinAction does not imply that you'll be polling for updates.