Trigger is a script that is launched when some event is happening. To create a new Trigger, open Scripts panel, click 
icon from the Toolbar and choose Add trigger option.
The code panel will be changed. Then, you need to:
- Define the Name for the Trigger
- Choose whether it is active now or not
- Set the Event when the Trigger is going to be executed
- Add Script — lines of code.
Before you start, visit wiki to get to know more about Memento Database syntax and view the Trigger examples.