演示：http://www.freejs.net/demo/524/index.html

<select class="demo" multiple="multiple">  
    <optgroup label="Languages">  
        <option value="cp">C++</option>  
        <option value="cs">C#</option>  
        <option value="oc">Object C</option>  
        <option value="c">C</option>  
    </optgroup>  
    <optgroup label="Scripts">  
        <option value="js">JavaScript</option>  
        <option value="php">PHP</option>  
        <option value="asp">ASP</option>  
        <option value="jsp">JSP</option>  
    </optgroup>  
</select>  
 

引用：http://www.freejs.net/article_biaodan_524.html