Today I was working on modernizing an xpages application when I came up with a simple enhancement: adding the optgroup tag to a xp:combobox.
By default this option is no available in XPages and if you look around there are some suggestions from hard-coded to DOM modification but I rather looked for a proper JSF implementation.
The data for my combobox resides in a categorized Notes view in a solid NSF so I had two options: navigating through the NotesView via a ViewNavigator (probably next post) or a quick and dirty combo of a dbcolumn and dblookup.
In context with the combobox control the dbcolumn/lookup combo seems suitable 
Here is the simplified setup for my xp:combobox:
As data source I am calling a method on a managed bean. The method is as followed:
The result is nice and straight-forward:
If you questions or difficulties with the implementation, just give me call. Happy development