title: What does a \ (backslash) do in PHP (5.3+)?
body: <p>What does a <code>\</code> do in PHP?</p>
  
  <p>For example, <a href="https://github.com/foxbunny/CSRF4PHP/blob/60d9172b7f0cd93346cac9065fb17182854ebf1c/CsrfToken.php#L80-L87" rel="noreferrer">CSRF4PHP</a> has <code>\FALSE</code>, <code>\session_id</code>, and <code>\Exception</code>:</p>
  
  <pre><code>public function __construct($timeout=300, $acceptGet=\FALSE){
      $this-&gt;timeout = $timeout;
      if (\session_id()) {
          $this-&gt;acceptGet = (bool) $acceptGet;
      } else {
          throw new \Exception('Could not find session id', 1);
      }
  }
  </code></pre>