title: What does "xmlns" in XML mean?
body: <p>I saw the following line in an XML file:</p>
  
  <pre><code>xmlns:android="http://schemas.android.com/apk/res/android"
  </code></pre>
  
  <p>I have also seen <code>xmlns</code> in many other XML files that I've come across.</p>
  
  <p>What is it?</p>