Ace comes with a few layers, but these don't behave as well as XP.
Layer 1 = autotiles (TileA)
Layer 1.5 = autotiles add-ons (like worldmap forests)
Layer 2 = add-ons (TileB through TileE).
Layer 3 = Events
You can only have 1 tile from each group on a tile grid. So, you can have a grass (Layer 1), a worldmap forest (Layer 1.5), a worldmap town (Layer 2), and an NPC standing on the town (evented Layer 3).
With the exception to the evented Layer 3, anything you touch as part of the map design will effect all tiles above. So if you decide that you want to change the grass to sand, it will wipe out the above layers and you will have to add them back in.