How do external layouts work? (expert level?)

My situation:
So I’m working on a procedurally generated dungeon and I’m not using the Dungeon Generator extension, coz it seems flawed. The extension doesn’t really fit the way I wanna generate dungeons, so I used the method described in gdevelop’s youtube video about procedurally generating levels/dungeons, the one titled the Binding of Isaac Generation.
https://youtu.be/OzjEQTEQwFg?t=118

Question is:
If you’re using checkers to create a new room, with new checkers by using external layouts, how does the engine know that it needs to place the room and not one of the room’s checkers on top of the old checker? Is it based on the size difference between a room object and a checker object?

Between my memory and a quick look at the video, each colored square or marker has it’s own for each object it adds the objects in the selected layout using the existing object referenced by the for each object. It repeats for each object of the color or marker it then deletes certain markers and then it repeats and does the same for the other markers.

What is your problem?

room_gen

There’s probably a typo somewhere. I can’t tell by the flashing gif. I’m tired and the text is flashing so fast that I can barely read it. Double check your events. I can’t tell without seeing the events. There are a lot of events. I don’t know what else to suggest at this moment.

Double check the events and layouts. If you’re still stuck maybe, you can post a screenshot of the specific area but I’m thinking you might have to upload your project to a files hare site and ask someone to check it. But I would recheck the events first.

I’m not stuck (yet). I just wanted to understand how the engine works. If you’re tired you should go to bed.

Did you check this example out?