The Observation module allows you to listen to events in the repository and trigger a reaction.
Use observation to automate tasks such as publishing newly added assets or sending an email notification when a comment is added. Custom event listeners can react to almost any event. The Observation module is based on the JCR observation feature.
Magnolia provides two types of event listeners: listeners that react to the event on their own and listeners that delegate the reaction to a command. Both listeners are configured the same way, but command event listeners require additional properties that the command class supports.