maplet

How is the " Custom" item used in maplet?

It's been a while since I used maplet, but if I remember correctly, you set the mode to copy then drag a box around the geometry you want to copy.

Then you can carve or fill with it.

Yes. But what is the custom item for?

Prefabs... create a staircase, then use it (as a custom item) to place copied staircases in other parts of your map