The online doc's show an example slave activity using trigger() to
activate the slave, but this doesn't work when the master is a
periodic activity. Reaons being that slave.trigger() ends up calling
master.trigger(), which simply returns false for a PeriodicActivity.
It does work if you call slave.execute() however. Am I missing
something here?

FYI, the unit tests for SlaveActivity all use execute() instead of
trigger(). Is it just the doc's that are incorrect?

Thanks
Stephen