placeholder
<body> <form method="post" action=""> placeholder <input name="email" type="text" placeholder="这里输入文字" size="22" /> <br> javascript <input name="mail" type="text" value="请输入内容" onfocus="javascript:if(this.value=='请输入内容')this.value='';"> <input type="submit"> </form> <hr> <?php var_dump($_POST); ?> </body>