title: JBOSS XML files understanding
body: <p>I used to be indifferent about the content of JBoss files. But now, I really would like to understand what would things mean ( double dots separator, urn, ... ).</p>
  
  <p>Here it is the snippet I would like to receive an explaination for :</p>
  
  <pre><code>&lt;subsystem xmlns="urn:jboss:domain:jgroups:1.2" default-stack="${jboss.default.jgroups.stack:udp}"&gt;
    ...
  &lt;/subsystem&gt;
  </code></pre>
  
  <p>Well, true this was taken from an Infinispan Server, but I would like to understand that tree <code>"urn:jboss:....."</code>. It is more about syntax interpretation way than what infinispan is trying to do.</p>
  
  <p>Thank you a lot!</p>