title: ejabberd server broadcast message
body: <p>In short, I want ejabberd server to send some messages to a group of user clients.</p>
  
  <p>the group of users may change. For example, the server send message to group 1, and then send different message to group 2.</p>
  
  <p>In other words, how to make ejabberd server send messages to client?
  I know how to send message from client to client.</p>