CKEDITOR and Those Darned <?php and ?> Tags

OPTION1: Covert specified char sequences back to their original state with str_replace

$content = htmlspecialchars($_POST['content'], ENT_QUOTES);

$turned = array( '<pre>', '</pre>', '<b>', '</b>', '<em>', '</em>', '<u>', '</u>', '<ul>', '</ul>', '<li>', '</li>', '<ol>', '</ol>' );
$turn_back = array( '<pre>', '</pre>', '<b>', '</b>', '<em>', '</em>', '<u>', '</u>', '<ul>', '</ul>', '<li>', '</li>', '<ol>', '</ol>' );

$content = str_replace( $turned, $turn_back, $content );

OPTION2: Use preg_replace

// $str is the result of htmlspecialchars() 
preg_replace('#&lt;(/?(?:pre|b|em|u|ul|li|ol))&gt;#', '<\1>', $str);