label标签主要用于绑定一个表单元素, 当点击label标签的时候, 被绑定的表单元素就会获得输入焦点
span则是对普通的文本的一种容器
示例：
<class="tags" href="/tags/DIV.html" title=div>div id="class="tags" href="/tags/DIV.html" title=div>divForm">
<class="tags" href="/tags/DIV.html" title=div>div class="class="tags" href="/tags/DIV.html" title=div>divFormItem">
<span>Did you visited my blog：</span>
<class="tags" href="/tags/INPUT.html" title=input>input type="radio" id="radYes" name="visitedblog" checked="checked" />
<label for="radYes">Yes</label>
<class="tags" href="/tags/INPUT.html" title=input>input type="radio" id="radNo" name="visitedblog" />
<span><label for="radNo">No</label>(Press the text "Yes" or "No" not the radio)</span>
</class="tags" href="/tags/DIV.html" title=div>div>
<class="tags" href="/tags/DIV.html" title=div>div class="class="tags" href="/tags/DIV.html" title=div>divFormItem">
<label accesskey="1" for="txtName">Your Name：</label>
<class="tags" href="/tags/INPUT.html" title=input>input type="text" id="txtName" value="Press Alt + 1" />
</class="tags" href="/tags/DIV.html" title=div>div>
</class="tags" href="/tags/DIV.html" title=div>div>
