[significantly rewritten Nov. 27]
AD&D planar space is defined in relation to the Ethereal or Astral plane. However, AD&D uses many words to define “other” dimensional space (non-dimensional, nonplanar, extradimensional, inter-dimensional, ultra-dimensional, non-spatial, non-space, nilspace), but does not clearly define how those relate to the Astral and Ethereal. The question is what’s the relationship (if any) between all of the different non-planar spaces? Let’s review various definitions of being somewhere other than “here”, to reach as close to a By the Book interpretation as possible:
- Bag of Holding: non-dimensional space
- Heward’s Handy Haversack: like Bag of Holding [non-dimensional space]
- Saddlebags of Holding (Dragon #208): As Bag of Holding [non-dimensional space]
- Girdle of Many Pouches: eight small pouches similar to a Bag of Holding [non-dimensional space]
- Hat of Holding (Dungeonland EX1): extradimensional space
- Bag of Devouring: “used by an extra-dimensional creature,” spitting contents out in non-space
- Portable Hole: extra-dimensional hole opens to a particular non-dimensional space
- Mirror of Life Trapping: non-spatial/extra-dimensional compartments
- Well of Many Worlds: inter-dimensional device casting occupant to another world or plane
- Rope Trick: “fastened in an extra-dimensional space”
- Gate: ultra-dimensional connection between two planes.
Divination spells contact powerful extradimensional creatures. Invocations are dedicated to powerful extradimensional beings. Given that both generally contact a deity, and the deities are located on the Outer planes, extradimensional is defining space beyond the Astral. Rings that call upon extradimensional creatures use conjuration/summoning, which could either be from the Inner or Outer planes (elementals/demons). The MoP refers to legends speaking of a plane far beyond known routes on the Ethereal, the home of all the extra-dimensional creatures that we believe to be Bags of Holding and Bags of Devouring.” In other words, descriptions use extradimensional in relation to both Ethereal and Astral associated planes, and thus are not specific to one or the other.
Astral space is defined as having no extradimensional component. Spells using extradimensional space will not function on the Astral, or be accessible. Dragon #67 even cautions that certain devices that use extra-dimensional spaces will expand abruptly in Astral space so that the exterior of the container conforms to match its interior capacity (Bag of Holding, Portable Hole). The Outer planes do have an extradimensional component, so spells that use nonplanar/extraplanar space (such as rope trick) function normally there. The MoP further clarifies that the Deeppockets spell uses extradimensional space and cannot be cast in the Astral plane, but will work from the Outer planes.
Extra-dimensional, non-spatial, and non-dimensional appear to be used interchangeably. More accurately, extradimensional and non-spatial are used to define space elsewhere, and non-dimensional refers to a specific discrete and unique space not associated with any other plane. With the exception of the Astral plane, it’s possible to reach extradimensional space regardless of the current plane.
An interesting point available for analysis is failures of the Bag of Holding and the Portable Hole:
- The contents of a pierced Bag of Holding end up in the “vortices of nilspace.”
- If a Bag of Holding is placed within a Portable Hole, a rift is torn to the Astral plane, and the bag and the cloth are sucked into the void and forever lost. In this context, the “void” is the rift to the Astral plane. See my article on the Astral Plane for how one might go about finding them again.
- If a Portable Hole is placed within a Bag of Holding, it opens a gate to a [random] plane, and the ‘hole, bag’ and any creatures within a 10′ radius are drawn onto the plane, the Portable Hole and Bag of Holding being destroyed in the process.
Three different possible outcomes. For the first, the contents are destroyed. In the second, they’re lost on Astral. For the third result the party itself is dragged along to parts unknown.
A Portable Hole is built from webs of a phase spider (Ethereal) with strands of ether and beams of Astral plane luminaries, and opens on its own particular non-dimensional space. If the Bag of Holding is towards the Ethereal and inner planes, and the Portable Hole is towards the outer planes (and Astral), that could explain the extreme results when you put the two together. The results must be similar to that of a violent ether cyclone, which creates temporary ruptures between the Astral and Ethereal, causing items to be lost forever to the vortices of nilspace. Note that in rare cases it is likely possible to reach into nilspace (or non-dimensional space) from a second connection. This is likely the source of the items in Zadron’s Pouch of Wonders (Dragon #62), a sort of magical grab-bag inside which a great variety of magic items can be found.