We’re not supplying server-side code, that’s something you’ll have to take care of yourself.
yeah, that is fine - but are there specifications or guidance as to what code or APIs I need to provide on the server ?
Nope. To do image uploads, you’ll have to set up your own upload service, and to save documents, you’ll need some kind of server-side code to do that, much like you would for a textarea. But the code in ProseMirror’s distribution doesn’t directly talk to a server, so how you implement this is entirely up to you.