… I don't know why I did most of the stuff in 8ab13c068133098bc17095ac7282b3e3d2e9e1f9 when this is, I think, simpler. Also means an EditRegionConfiguration is mostly aware of everything it needs to be, rather than being fed things that it may or may not consider valid.

Works because of commits 7512322378e6364ea7a107c274e42c157f36c797 and 876a6c9626c3e86ead843371279c6450cf84314f