In.php

<?php

/*
 * This file is part of Twig.
 *
 * (c) 2010 Fabien Potencier
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
class Twig_Node_Expression_Binary_In extends Twig_Node_Expression_Binary {

  /**
   * Compiles the node to PHP.
   *
   * @param Twig_Compiler A Twig_Compiler instance
   */
  public function compile(Twig_Compiler $compiler) {
    $compiler
      ->raw('twig_in_filter(')
      ->subcompile($this
      ->getNode('left'))
      ->raw(', ')
      ->subcompile($this
      ->getNode('right'))
      ->raw(')');
  }
  public function operator(Twig_Compiler $compiler) {
    return $compiler
      ->raw('in');
  }

}