Using underscore (_) as a PHP function name
<p>According to <a href="http://php.net/manual/en/functions.user-defined.php" rel="nofollow">http://php.net/manual/en/functions.user-defined.php</a>, I should be able to use an underscore (_) as a function name:</p>

<blockquote>
  <p>Function names follow the same rules as other labels in PHP. A valid
  function name starts with a letter or underscore, followed by any
  number of letters, numbers, or underscores. As a regular expression,
  it would be expressed thus: [a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*.</p>
</blockquote>

<p>However, the following kills my program without causing any errors:</p>

<pre><code>error_reporting(E_ALL);
echo('start');
function _($x){return ($x)?htmlspecialchars($x):'nbsp;';}
echo('end');
</code></pre>

<p>I am using PHP Version 5.3.18. What don't I understand?</p>
