Selection/Range/Caret like in Google Docs, CodeMirror and Ace Editor (Cloud9 IDE)?

Question

JavaScript

Friends, has anyone had experience implementing custom selection in JS? I want to implement similar functionality (I use Google Closure), but I still don’t understand how it should work. Started digging around with the CodeMirror and Ace sorters, but any help and thoughts on this would be greatly appreciated as well. Perhaps someone will be able to push where to drip.