Using a partial CUIX file to add ribbon bar elements for your application is required, but how you do this will depend on your plug-in design. As a minimum, every plug-in or block library must add a panel to the Plug-Ins tab that either invokes the main command defined by the plug-in or displays a helpfile explaining how to use the block library. The DevTV–Creating a Partial CUI video posted with these guidelines shows how to setup a partial CUIX file to add a panel to a tab already defined in the main CUIX.
Plug-ins that install a single panel should normally add that panel to the Plug-Ins tab.
Plug-ins that create several ribbon bar panels may prefer to create a new tab specific to that plug-in (and normally with the tab name being the name of the plug-in).
You can add any other UI elements to your partial CUIX (for example, menubars and toolbars) as well, but you must still include a basic ribbon bar UI.