These events are to do with the control/feedback of the zone master.
General
A zone master is responsible for control of anything that is used by multiple zone groups.
http://id.webbrick.co.uk/zones/master
This is the event type for all events to do with the master zone.
zone/master/run
This event source indicates a requirement to run any devices required by the zone groups.
zone/master/stop
This event source indicates there is now no requirement to run any devices required by the zone groups.
zone/master/running
This event source indicates that the zone master is running.
zone/master/stopped
This event source indicates the zone master has stopped.