title: Unknown pattern character 'x', when using SimpleDateFormat
body: <p>Im trying to format a <code>Date</code> to <code>String</code> using <code>SimpleDateFormat</code>, and the pattern im using is this one </p>
  
  <blockquote>
    <p>"yyyy-MM-dd'T'HH:mm:ss.SSSxxx"</p>
  </blockquote>
  
  <p>but when reach this line</p>
  
  <pre><code>SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSxxx");
  </code></pre>
  
  <p>i get the following exception:</p>
  
  <blockquote>
    <p>java.lang.IllegalArgumentException: Unknown pattern character 'x' at
    java.text.SimpleDateFormat.validatePatternCharacter(SimpleDateFormat.java:323)
    at
    java.text.SimpleDateFormat.validatePattern(SimpleDateFormat.java:312)
    at java.text.SimpleDateFormat.(SimpleDateFormat.java:365) at
    java.text.SimpleDateFormat.(SimpleDateFormat.java:258)</p>
  </blockquote>
  
  <p>the format im trying to achieve is 
  "<strong>2017-06-16T12:19:59.001+02:00</strong>"</p>
  
  <p>according to the <a href="https://developer.android.com/reference/java/text/SimpleDateFormat.html" rel="noreferrer">documentation</a> this pattern should work
  Whats wrong?</p>
  
  <p><strong>EDIT</strong>
  To clarify, i tried with xxx and XXX</p>
  
  <p>in case of XXX i get java.lang.IllegalArgumentException: Unknown pattern character 'X'</p>