<!DOCTYPE html> 
<html> 
<head> 
 <meta charset = "utf-8"> 
 <title>demo</title> 
 <link href="bootstrap-3.3.4-dist/css/bootstrap.min.css" rel="stylesheet"> 
 <style type="text/css"> 
  body{padding: 20px;} 
 </style> 
</head> 
<body> 
 <form role = "form"> 
  <div class="form-group col-lg-3 form-horizontal"> 
   <label for = "idCard" class="control-label col-lg-5">身份證號(hào)：</label> 
   <div class="col-lg-7"> 
    <input type = "text" id = "idCard" class="form-control"> 
   </div>   
  </div>  
 </form> 
</body> 
</html>

但是如果我們沒(méi)有給輸入框設(shè)置label時(shí)，當(dāng)其獲得焦點(diǎn)時(shí)，屏幕閱讀器會(huì)讀出aria-label屬性的值，aria-label不會(huì)在視覺(jué)上呈現(xiàn)效果。
如：

<body> 
 <form role = "form"> 
  <div class="form-group col-lg-3 form-horizontal"> 
   <div class="col-lg-7"> 
    <input type = "text" id = "idCard" class="form-control" aria-label = "身份證號(hào)"> 
   </div>   
  </div>  
 </form> 
</body>

aria-labelledby屬性

當(dāng)想要的標(biāo)簽文本已在其他元素中存在時(shí)，可以使用aria-labelledby，并將其值為所有讀取的元素的id。如下：
當(dāng)ul獲取到焦點(diǎn)時(shí)，屏幕閱讀器是會(huì)讀：“選擇您的職位”

<body> 
 <div class="dropdown"> 
  <button type="button" class="btn dropdown-toggle" id="dropdownMenu1" 
   data-toggle="dropdown"> 
   選擇您的職位 
   <span class="caret"></span> 
  </button> 
  <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1"> 
   <li role="presentation"> 
    <a role="menuitem" tabindex="-1" href="#">測(cè)試工程師</a> 
   </li> 
   <li role="presentation"> 
    <a role="menuitem" tabindex="-1" href="#">開(kāi)發(fā)工程師</a> 
   </li> 
   <li role="presentation"> 
    <a role="menuitem" tabindex="-1" href="#">銷售工程師</a> 
   </li>   
  </ul> 
 </div> 
</body>