The editor itself is still pretty crude, but - like most of my own personal projects - it's functional enough to demonstrate how it would work.
Of course, with a bit of SteveMagic, it'll really look the biz, but for now it's simple enough. Select either the floor tile or wall type you want to place, and click into the HTML5 canvas area. Using some simple array sorting and some bitmap blitting, the map is redrawn each time a tile (or wall) is placed or removed.
A bit of simple string splitting and a "instantiate" calls later, and our map is recreated from our flat HTML5 web page into our 3D game environment. All very exciting stuff. A bit boring and repetitive to give full code listing here (and if you really must, you can always "view source" on the map editor screen) but at last it feels like we're making progress with this whole "let's-put-the-game-into-a-3d-environment-we've-never-used-before" idea!