The originate_continue_on_timeout is set to true for this: if the bridge's dial string specifies several destinations separated by the "|" (this is for failover), the bridge will time out on an unanswered destination and will attempt the next specified destination.
The continue_on_fail is set to true for this: if the bridge fails, dialplan execution will continue and the transfer will be executed.
The hangup_after_bridge is set to true for this effect: if the bridge is successfully answered and the B-leg later hangs up, the A-leg will also be hung up.
To explain the variables set prior to the bridge: The extension 200 will ring all the users defined in the user directory for group 200 in a serial fashion (specified by the +F argument, if you want to ring all the users at once use the +A argument) for 15 seconds, then it will transfer the call to the same group again so the call will ring the group infinitely.