Can anyone tell me what a "master public key" is? There's a menu item that says "copy master public key to clipboard." What is that number good for?
This is one way to run a web server with merchant ability. Having the watch only wallet on the server allows it to generate new addresses and receive payments without the ability to have them spent. Any refunds or "spends" would be done on another computer, with full wallet, not related to the web server.
For merchants, there is a script on github using Electrum to do this. I've also created a variant using only a mysql table rather than jsonrpc calls.