A roster, in XMPP-speak, is your friends list. Now imagine that you log in to your IM network for the very first time and everyone you know is already on your contact list, neatly arranged into different groups such as 'Friends', 'Office', and so on. That's the magic of pre-populating rosters.
To get the most out of this section, I'll show you a couple of examples that you will be able to identify with. Let's picture a typical office scenario with several users arranged into three groups:
James, Nicole, Rob, Dale, Carla
Henry, Peter, Sally
Now let's use these users and groups in our hypothetical (but very practical) examples.
This is the most logical ...