The web builds use Emscripten + SDL2, and I've thus far been unable to open the on-screen keyboard for typing code.
For playing games, I could add some touch buttons if the browser reports a mobile platform, but for this to work well I would need to accommodate the screen's aspect ratio properly -- conceptually a trivial problem, but resizing the JS canvas can be unreliable seemingly (and, in itch's case, the game is in a fixed-sized iframe anyway).
