We are able to add the injected separator to both ribbon and menus. 

Notice that we are able to set visibility at separators. 

Separator in ribbon

To add a separator in ribbon, use this command between your buttons or menus. You can add it in an individual module at the end or in the beginning, or in between buttons. 

<separator id="separator"/>

As an example, here is how it looks in ribbon:

Separator in menus

To add a separator in a menu, this command must be used between two buttons in the menu (note that it is an injected feature):

<Inject>
 <menuSeparator id="separator"/>
</Inject>

This is how it looks in a menu: