What technology does Google Drive use to do real-time?

When I type in a Google Drive document that is being accessed by multiple users, the Chrome Developer Tools Network tab shows that there are no WebSockets.

I see that the two most frequent types of AJAX call have either "bind?" or "save?" in the URL. "save?" POST requests are made every time I type, which makes sense- normal AJAX for sending updates to the server.

When another user types, the most recent "bind?" GET call stays open, and the amount of data transferred over that connection increases. Periodically, "bind?"s are closed and new ones open up, and the logic seems to be some function of duration and data size. 

This isn't long-polling, since when the server sends updates it doesn't complete the response.

This doesn't seem to be server-sent events, since the content-type is "text/plain" instead of "text/stream".

Is there a name for what Google is doing? If so, how can I try implementing this?

[![Chrome Dev Tools - editing a Google Drive document](https://i.stack.imgur.com/AqkMu.png)](https://i.stack.imgur.com/AqkMu.png)