Actually I think the 'ace' in Paper/Hackpad/Etherpad is a different thing called ace.
https://github.com/ether/pad/tree/master/infrastructure/ace
> ACE2 is EtherPad's editor, a content-editable-based rich text editor that supports IE6+, FF(2?/)3+, Safari(3?/)4+. It supports collaborative editing using operation transforms (easysync2), undo/redo, copy/paste.
> The name "ACE2" is because this is a rewrite of aiba's original content-editable AppJet Code Editor.