Two portable holes would rupture if one were inside the other, right?

Question

The Dungeon Master's Guide, on page 187, says:

Placing a portable hole inside an extradimensional space created by a bag of holding, Heward's handy haversack, or similar item instantly destroys both items and opens a gate to the Astral Plane.

A portable hole is a "similar item" to another portable hole.

Thus, if one puts one portable hole inside another portable hole, they are both destroyed, right?

The rules about combining extradimensional objects seem to be very strict in 5th Edition, but this rule seems to be vaguely worded. I guess the intent is to discourage the use of combinations of extradimensional items, and to punish careless players.

If, on the other hand, there is some reason to stress that each item is only incompatible with items of other designs, then the rule means that each portable hole is compatible with every other portable hole.

Answer 1

Yes, a portable hole is a "similar item," and when put into another portable hole will destroy both and create a planar rupture.

It's the "nesting" of extradimensional space that causes the havoc, not any properties particular to these magic items individually or as a set.

Note however that there is something particular to the kind of extradimensional space attached to these items: the nesting problem only manifests relative to extradimensional space created by such magic items. They'll all play havoc with each other, but you don't have to be paranoid simply carrying such items into other planes, pocket dimensions (natural or spell-created), and the like. Whatever space these items connect to, it's not the kind of space you can wander into unknowingly while planeswalking.