title: PHP validate ISO 8601 date string
body: <p>How do you validate ISO 8601 date string (ex: 2011-10-02T23:25:42Z).</p>
  
  <p>I know that there are several possible representations of ISO 8601 dates, but I'm only interested in validating the format I gave as an example above.</p>
  
  <p>Thanks!</p>