The MicroStationAPI help contains an extensive discussion of the MicroStation CONNECT Ribbon interface: search for Ribbon Bar Interface. There are plenty of examples in XML format.
Prompted by this question in the MicroStation Forum, I wonder if it's possible to apply a template to Ribbon objects. In this case, is there such a thing as a group template that would let a MicroStation user set a consistent size and appearance of all groups? An analogy is the XAML control template.