Extra-dimensional, non-dimensional and the planes

[Altair_the_Vexed]

Extra-dimensional, non-dimensional and the planes: these terms get used a fair bit in D&D.
Rope trick uses an extradimensional space outside the multiverse of extradimensional spaces. It says that

"It is hazardous to create an extradimensional space within an existing extradimensional space or to take an extradimensional space into an existing one."

The best description of what happens in such a case is in the descriptions of the portable hole and bag of holding...

What I'm looking for is some sort of definition of the terms. Has any been published?
The most practical questions to do with the definitions that I have are:

• Is an extradimensional space a "plane"?
• Can you teleport from an extradimensional space to a point on the plane from which you opened the space?
• What is it about the portable hole and bag of holding that makes them incompatible, while there isn't any note about holes inside holes or bags inside bags?

[jiriku]

1) An extradimensional space is not a plane. It is the inside of any container that's bigger on the inside than it is on the outside, or any location that has zero external dimensions (such as rope trick or mordenkainen's magnificent mansion).

2) You can't teleport out of an extradimensional space, but you could plane shift out of one. However, you can't plane shift into one, because, as defined above, it's not a plane.

3) As for why there's no rule against putting a bag inside another bag, I suppose it's probably because it just didn't occur to the original 1st edition designers, and sometimes these things just get passed down from edition to edition like that.


FYI, the 3rd ed manual of the planes basically BEGS you, as DM, to make up whatever the heck you want for your own cosmology and define these things as you see fit, so if you're the DM and you want to do things differently, WotC is totally onboard with that.

[PairO'Dice Lost]

Originally Posted by Altair_the_Vexed

* What is it about the portable hole and bag of holding that makes them incompatible, while there isn't any note about holes inside holes or bags inside bags?

Originally Posted by jiriku

As for why there's no rule against putting a bag inside another bag, I suppose it's probably because it just didn't occur to the original 1st edition designers, and sometimes these things just get passed down from edition to edition like that.

In fact, it did occur to the 1e designers. Originally, any extradimensional space put into any other extradimensional space caused terrible things to happen, but they were removed and/or ignored as editions progressed, as evidenced by the rope trick text being a direct copy-paste from the 1e/2e version even though the rules for it were removed in 3e. The bag of holding/portable hole combo was interesting in that what happened changed based on which was put in which, so that was the most memorable of the interactions and thus was most likely kept because the designers thought it was iconic.