I just stumbled upon this mod and was very intrigued with it. I have had no trouble using it with the vanilla dims and the modded dims but when I add a custom dim in the stacked dimension menu in world creation it calls it undefined and when I open the world and try to enter the dim the blocks won't break and it won't let me inter the new dim. I've been looking for a tutorial for this and haven't been successful. Is there something else I need to do to the added dim before World creation to make it functional? This mod is pretty awesome and I would like to get this to work. I am simply trying to make another dim that is all stone with vanilla and modded gens. I left it at the max height of 255. Expected blocks are minecraft:stone and a transition of 16, Probably doesn't need to be that much but that's what I put on all the dims. I even made one and reduced the height to 144 and still didn't work. Please add a tutorial for this in the wiki or if their is one point my blindness in the right direction. Thank you for this wonderful mod.

Adding dimensions is now implemented and will be in next release:

1. Enter an unused dimension id to add Dimension.
2. Select it to the right list using Select button.
3. Click Edit Dimension
4. Change the bottom left button to Create Dimension: Yes. The dimension is now named dimstack_custom instead of undefined.
5. Click on the newly appeared Dimension Creation button to configure its properties.
6. Enter a biome name/id if you want a single biome instead of normal overworld biome generation.
7. The chunk generator Empty World is recommended for sky, void or mining dimensions. Use block layers and other generation features to fill them with stuff.

TODO: add some aesthetic configuration options for created dimensions like fog colors, sky colors, brightness, horizon and cloud height.

Currently the mod can't add new dimensions itself but that is a planned feature.

So the "add dimension" button in the menu does not actually create a new dimension. It's purpose currently is to manually add existing dimensions that are not automatically recognized by the mod. These are for example ones that are not defined until a world is actually created and loaded, like RF-Tools Worlds.