title: What is the difference between RFC1123 and RFC2822 DateTime formatting in PHP?
body: <p>This is out of curiosity rather than because I need to know it at this point, but in the PHP manual, they're identical; I can't see the reason that there are two different data formats for the same thing.</p>
  
  <p><a href="http://php.net/manual/en/class.datetime.php">http://php.net/manual/en/class.datetime.php</a></p>
  
  <pre><code>const string RFC1123 = "D, d M Y H:i:s O" ;
  const string RFC2822 = "D, d M Y H:i:s O" ;
  </code></pre>
  
  <p>Any clue?</p>