Connection lost. Saving has been disabled until you’re reconnected. We’re backing up this post in your browser, just in case

Had counter this when saving a wp post/page? "Connection lost. Saving has been disabled until you’re reconnected. We’re backing up this post in your browser, just in case."

I'm interest what kind of tech wp use for backup the data into browser, specially using php. What did the ment, saving into XML in browser cache? raw data? Or another technology? All the browser can do that? I've google no luck.

Enlight me bro. Thanks.