I want to trigger a function when an object crosses the border of the level. So I used a StaticBody2D with a CollisionPolygon2D, with trigger
set to true.

According to the documentation:
A trigger polygon detects collisions, but is otherwise unaffected by physics.
But, how do I trigger a function when an object crosses it?

I tried to connect a signal to the StaticBody2D but there is no "body_enter" signal...
I can detect the collision from all kinds of objects instead (ugh), but then, what is the trigger
property for?