//I was wondering - what exactly is a pocket dimension, and how would it be created/gained access to? What are the "rules" for pocket dimensions?
Are we talking temporary ones like Mordenkainen’sMagnificent Mansion or permanent ones? Those that belong where they are? Movingones? Those of a mage or a deity? A specific spell? Bags of holding? Portableholes? Extra-dimendional? Non-dimensional? Demi-planes? Also how big are wetalking about? A Familiar Pocket or a Bag of Holding? It depends on each pocketif it can even be liveable.
Generally speaking, however, a pocket dimension is a separateplane of existence or an isolated area of a plane. Its entry point remains stationary and fixed to a location(…exceptwhen it’s not and it’s tied to other places via portals or by portal key) or particularsituations (like a summer solstice or humming while walking between trees that look like an archway)
It usually cannot be penetrated or escaped from except throughthe entrance. There are ways of outside access via powerful spells but again,it varies from dimension to dimension. Each pocket can have its own planartraits. They can be created via powerful spells or deities and some evolvenaturally.