[Observium] How does SYSLOG Alerting work?

Hello! Thanks for higly awaited feature with SYSLOG alerting! Just playing with it, I was unable to make it working (of course, with knowledge of PCRE). The example of my test Alert was based on *SYS-5-CONFIG_I:Configured* message from IOS router. Can you advice on how the regexp should look like and how does SYSLOG Alerter work - on a poll or triggered on a log receipt? -- Best, Sergey