How does HP's "Scan to computer" feature work?

How does HP's "Scan to computer" feature work?

Many HP all-in-ones have a "Scan to computer" function where you can be
standing at a network printer and scan all your gubbins straight to your
computer without having to load up scanning applications. This is
particularly useful if the computer and scanner are in different rooms.
The problem is HP's open source driver doesn't provide this functionality
for Linux and that's a real problem for me because it's Linux only here.
I'd like to implement the functionality but I don't know what sort of APIs
they're using, how the computers are handshaking with the printer (to show
their availability) or anything really about how the scans are sent.
Is there any documentation (official or otherwise) on how "Scan to
computer" works?