增量状态栏通知图标

You know what I'm talking about: for example when you get multiple new emails the notification icon in the status bar is augmented with a little red circle that contains number of unread mails. Twitroid has the same icon. Any idea how it's done? I don't think (or so I hope) there are 10000 similar icons. Is this red circle generated and overlaid the notification icon? If so - any code snippets will be much appreciated.You know what I'm talking about: for example wh