Dimensionalism is a relatively recent school of arcane magic, formed within the last century. Founded by Deverick Abraxas on a little-known Prime world, the extradimensional basis of the school quickly led to it spreading throughout the planes, many finding the various spells quite handy to have while traveling through the multiverse. The school has changed greatly since its original form, however. Originally serving as a more general-purpose extraplanar school, including spells to deal with extraplanar creatures (conjure elemental, invisible stalker, summon shadow), spells to manipulate extraplanar substance (demi-shadow magic, move earth), and spells that among other things are simply useful to spot extraplanar phenomena (true seeing) , within a few decades it had stabilized around those spells specifically related to the distortion or manipulation of space, time, and dimension.
There are theories by some that the shift in Dimensionalism over the years may be due to the influence of chronomancers, due to the similarity in focus of the two schools of magic, but given the secretive nature of that sect of wizards, there is little proof. Or rather, there may have been proof at some point, but it currently does not seem to have existed.
- Dragon #229 - The Dimensional Wizard, pp.51-52