此处input为什么要添加span父级呢?有什么好处么?
<div class="sign-input"> <span>帐 号:</span> <span><input autocomplete="on" name="u" id="u" type="text" style="ime-mode: disabled" class="input01" tabindex="1" value="QQ号码或Email 帐号" onFocus="if (value =='QQ号码或Email帐号'){value =''}" onBlur="if (value ==''){value='QQ号码或Email帐号';}" /></span> </div>