代码示例:(标识:hdom_select_multiple)
<html>
<head>
<script type="text/javascript">
function selectMultiple()
  {
  document.getElementById("mySelect").multiple=true
  }
</script>
</head>
<body>

<form>
<select id="mySelect" size="4">
  <option>苹果</option>
  <option>桃子</option>
  <option>香蕉</option>
  <option>桔子</option>
</select>
<input type="button" onclick="selectMultiple()" value="选择多个">
</form>
<p>在您点击 “选择多个” 按钮之前,请尝试同时选取多个选项。在点击 “选择多个” 按钮之后,请再试一次。</p>

</body>
</html>
运行结果: