bootstrap中的下拉菜单

下拉菜单必要的代码：

                            <div  class="container">

                                     <div  class="dropdown">

                                            <button  class="btn  btn-default  dropdown-toggle" id="aa"  data-toggle="dropdown"  aria-expanded="true">

                                                     按钮</button>

                                            <ul  class="dropdown-menu"  role="menu"  aria-labelledby="aa">

                                                   <li><a  href="">菜单1</a></li>

                                                   <li><a  href="">菜单2</a></li>

                                           </ul>

                                 </div>

                          </div>

 可在下拉列表中插入的内容有：a,分割线：<span  class="glyphicon   glyphicon-xxx"  aria-hidden="true"></span>

                                        b,提示信息：<li  role="presentation"  class="divider"></li>

                                        c,默认不能点击：<li  role="presentation"  class="disabled"><a href="jarascript:voidco">xx</a></li>