title: Meaning of [Z] in format + string in Moment.js
body: <p>I am wondering what this does:</p>
  
  <pre><code>newM = moment("2015-08-11T13:00:00.000000Z", "YYYY-MM-DDTHH:mm:ss.SSSS[Z]", true)
  </code></pre>
  
  <p>Specifically - the [Z] in the format string.</p>
  
  <p>I am using a library (react-bootstrap-datetimepicker) which uses moment. This library (React component) takes a parameter 'format' which is used as the second parameter to moment</p>
  
  <p>I can't see what the [Z] is doing. But I have to do this rather than just 'Z' to get the result I want when I format the moment object for display with this string: newM.format('YYYY-MM-DD HH:mm:ss.SSSZ'). </p>
  
  <p>EDIT:</p>
  
  <p>to be clear: I understand that 'Z' will cause the datetime passed to be treated as UTC, as per the docs. But what is the significance of the square brackets - which are not in the docs.</p>