Element: [NavMenu]导航条中添加split分割下拉菜单

[mogocat]

目前还没看到这个框架中有这个功能。按钮的下拉菜单中可以这样设置，但是导航条中不行，不知道导航条里怎么做这种效果。

http://jsfiddle.net/api/post/library/pure/

我需要在导航条中，使用右边那种按钮的效果。即：父按钮可以点击，打开下拉菜单，子按钮也可以单独点击。

[element-bot]

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