title: what is the use of xsi:schemaLocation?
body: <p>I see that we have multiple url's as value of this attribute like in spring:</p>
  
  <pre><code>&lt;beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:aop="http://www.springframework.org/schema/aop"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
  http://www.springframework.org/schema/aop
  http://www.springframework.org/schema/aop/spring-aop-2.0.xsd"&gt;
  </code></pre>
  
  <p>Why is it needed and what is it used for? Does Spring goes to the url and validate? 
  what is the difference between xmlns and xsi:schemaLocation?</p>