Enable a node's menu item when on that node? /2,if same path

// Answer for question on Drupal Stack Exchange:
// http://drupal.stackexchange.com/questions/27907/enable-a-nodes-menu-item-when-on-that-node

/**
 * @see http://api.drupal.org/api/drupal/includes%21menu.inc/function/theme_menu_link/7
 */
function YOURTHEMENAME_menu_link(array $variables) {

  $element_can_be_visible_on_node_id = 9; // SUBSTITUTE IT with your node's id!!
  $your_path_to_hide = 'node/'.$element_can_be_visible_on_node_id; // SUBSTITUTE IT with yours (when using nodes, use it like this: 'node/9', etc.!)
  $is_element_to_hide = ($variables['element']['#href'] == $your_path_to_hide);
  if($is_element_to_hide){
    $element_can_be_visible = (arg(0)=='node' && arg(1) == $element_can_be_visible_on_node_id);

    if(!$element_can_be_visible){
      return '';
    }
  }

  $element = $variables['element'];
  $sub_menu = '';

  if ($element['#below']) {
    $sub_menu = drupal_render($element['#below']);
  }
  $output = l($element['#title'], $element['#href'], $element['#localized_options']);
  return '<li' . drupal_attributes($element['#attributes']) . '>' . $output . $sub_menu . "</li>\n";
}