Drupal7中的und是什么

在Drupal7专业开发指南 第三版里看到了这么一段代码：

/**
 * Implements hook_validate().
 * 数据校验
 */
function job_post_validate($node)
{
    // Enforce a minimum character count of 2 on company names.
    // 公司名至少2个字
      
    // 测试一下und是个什么东西
    print_r($node);
    form_set_error('job_post_company', t('只是测试一下.'), $limit_validation_errors = NULL);
      
    if(isset($node->job_post_company) && strlen($node->job_post_company['und'][0]['value']) < 2)
    {
        form_set_error('job_post_company', t('The company name is too short. It must be atleast 2 characters.'), $limit_validation_errors = NULL);
    }
}

$node->job_post_company['und'][0]['value'])里面的und不太好理解，所以干脆打印出来看了看，发现是这么一堆东西：

stdClass Object
(
    [nid] => 
    [vid] => 
    [uid] => 7
    [created] => 1372676228
    [type] => job_post
    [language] => zh-hans
    [changed] => 
    [title] => 招聘程序员
    [additional_settings__active_tab] => 
    [revision] => 
    [log] => 
    [name] => demo
    [date] => 
    [status] => 1
    [promote] => 1
    [sticky] => 0
    [submit] => 保存
    [preview] => 预览
    [body] => Array
        (
            [und] => Array
                (
                    [0] => Array
                        (
                            [summary] => 
                            [value] => 啊啊啊啊啊啊啊啊啊
                            [format] => filtered_html
                        )
   
                )
   
        )
   
    [job_post_company] => Array
        (
            [und] => Array
                (
                    [0] => Array
                        (
                            [value] => 帝都公司
                        )
   
                )
   
        )
   
    [form_build_id] => form-JztE_Qw-WrP5bnVKgO8TkrjKC3Af8DWnb3uO0JdvhXA
    [form_token] => AYii6Gm9ObHt1HQaBKD0Fz0woRpDetFsUBcSgO97aeY
    [form_id] => job_post_node_form
    [comment] => 2
    [menu] => Array
        (
            [enabled] => 0
            [mlid] => 0
            [module] => menu
            [hidden] => 0
            [has_children] => 0
            [customized] => 0
            [options] => Array
                (
                )
   
            [expanded] => 0
            [parent_depth_limit] => 8
            [link_title] => 
            [description] => 
            [parent] => main-menu:0
            [weight] => 0
        )
   
    [path] => Array
        (
            [alias] => 
            [pid] => 
            [source] => 
            [language] => und
        )
   
    [op] => 保存

und这个键就一目了然了。从单词上来讲，und似乎是undefined的缩写。有一篇帖子http://drupal.stackexchange.com/questions/25839/best-practice-for-drupal-7-language-key-for-und-in-hook-form-alter 写道不应该硬编码und，因为这个键并不一定是und，似乎根据语言变动。帖子里有个人说应该这么写

function my_module_form_alter(&$form, &$form_state, $form_id) {
  
  if ($form_id == "someID") {
// 硬编码是不对的
     $form['field_charity_author']['und'][0]['value']['#value'] = arg(3);
  
// 应该这么写
$field_language = field_language('node', $node, 'field_charity_author');  
$form['field_charity_author'][$field_language][0]['value']['#value'] = arg(3);
  }
}

自己倒不是很明白，看了帖子也不太明白，模模糊糊地感觉这玩意儿是个败笔，就这样。

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