And how would you do that, if you don't mind answering a beginner like me ? x)
<rect x='0.0' y='0.0' width='1.0' height='1.0' />
Change X and Y to set the top-left co-ordinate from the event's top left.
Change width and height to the size of the rectangle.
So if you want a massive rectangle that is 200 tiles tall, 1 tile wide you could have:
<rect x='0.0' y='-100.0' width='1.0' height='200.0' />
Or 200 tiles wide, 1 tile tall:
<rect x='-100.0' y='0.0' width='100.0' height='1.0' />
You can also do lines (generally Player Touch is needed to activate these):
<line x1='0' y1='0' x2='1' y2='1' />
Polygons (each point pair must be clock-wise winding and polygon convex):
<polygon points='0.0,1.0 0.5,0.0 1.0,1.0' />
And regular Polygons (this example makes a tile-sized pentagon):
<regular cx='0.5' cy='0.5' rx='0.5' ry='0.5' p='5' />
You can make a collection of colliders by having a shape on each line between the <collider></collider> tags, so you can have very complex shapes that cover a crazy complex area if you want.