It would be extremely convenient to allow for certain user-defined planes to be togglable in the .dmm editor, much the same as each atom is. This would help a lot for complex level design situations.

And while we're at it, having the plane variables like color and alpha which translate to the .dmm editor from an atom would be nice as well.

For example, mapping some nice little paralaxxed water effects for Haz, if I have the ocean alpha set to 128 on the type definition it will have that show in the dmm editor. If I have the plane alpha set to 128, it will show as opaque.

I know that technically planes are special and they are used by the renderer in Dream Seeker and that it wouldn't be the most straightforward thing to plug into the dmm editor, but like I said, it'd be hugely convenient for larger projects that make use of these things.