I am currently working on a web based version of such an editor at JetBrains. You can take a look at it here: http://jb-proj-demo.appspot.com/ (It's open source and it's available on github here: https://github.com/JetBrains/jetpad-projectional)
We have quite a smart layout here which was implemented from scratch.
I am currently working on a web based version of such an editor at JetBrains. You can take a look at it here: http://jb-proj-demo.appspot.com/ (It's open source and it's available on github here: https://github.com/JetBrains/jetpad-projectional)