title: Is 'xmlns:web' attribute special in XML?
body: <p>A lot of examples of Java EE's <code>web.xml</code> file begin with</p>
  
  <pre><code>&lt;web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns="http://java.sun.com/xml/ns/javaee"
      xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" &lt;----------
      xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                          http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 
      id="WebApp_ID"
      version="2.5"&gt;
  ...
  </code></pre>
  
  <p>While I think I understand <a href="http://www.w3.org/TR/REC-xml-names/#ns-decl" rel="nofollow noreferrer">what 'xmlns:anything' generally means</a> and I suppose <code>xsi:schemaLocation</code> is just a map <code>XML namespace -&gt; schema file (XSD?) URI</code> I don't know what <code>xmlns:web</code> is supposed to mean.</p>
  
  <ol>
  <li><p>Is it a declaration of <code>http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd</code> namespace with <code>web</code> prefix? If it is so, why the prefix is not used in most of the examples? And why the namespace ends with '.xsd' -- this being nonstandard?</p></li>
  <li><p>If it is a declaration of schema location for the default namespace, where can i find documentation for this feature?</p></li>
  </ol>
  
  <p>Example of examples:</p>
  
  <ul>
  <li><strong>every</strong> 'Dynamic Web Project' created by Eclipse</li>
  <li><a href="http://docs.oracle.com/cd/E14571_01/web.1111/e13712/web_xml.htm" rel="nofollow noreferrer">http://docs.oracle.com/cd/E14571_01/web.1111/e13712/web_xml.htm</a></li>
  <li><a href="https://stackoverflow.com/questions/10829350/newbie-web-xml-eclipse-xsischemalocation-xmlnsweb">Newbie: Web.xml Eclipse. xsi:schemaLocation &amp; xmlns:web</a></li>
  <li><a href="http://en.wikipedia.org/wiki/Apache_Wicket" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Apache_Wicket</a></li>
  <li><a href="http://scn.sap.com/community/open-source/blog/2012/05/02/nw-73-spring-31-jsf-20-and-primefaces-part-2" rel="nofollow noreferrer">http://scn.sap.com/community/open-source/blog/2012/05/02/nw-73-spring-31-jsf-20-and-primefaces-part-2</a></li>
  </ul>