A good extensive article, in laymans language ...worth a look.
<a class="postlink" href="http://maineblue.co.uk/2012/08/27/liverpool-arsenal-and-united-join-the-self-preservation-society-2/" onclick="window.open(this.href);return false;">http://maineblue.co.uk/2012/08/27/liver ... society-2/</a>