Google Drive Realtime API developer here. https://developers.google.com/drive/realtime/
If you're trying to build your own Google Docs, you might want to consider using the Drive Realtime API, which is based on the same technology as Google Docs.
The Drive Realtime API has a wide range of mutations built in for common data structures: - Maps (last writer wins) - Lists (insert, delete, overwrite) - Strings (insert, delete, overwrite)
We also support arbitrary data structures including trees and graphs.
For modeling cursors, we have "Index References" which are effectively pointers to a specific element in a string or list. You can move them around on the client side and we have all of the transformation logic worked out so that concurrent edits don't make them point at the wrong position.
Because the data is stored in Google Drive, you can create, share and organize files using the standard functions in the Google Drive API. There's also an easy-to-use REST API for importing and exporting data as JSON.