woeful rivet
1 - As a vassal, when I acquire a higher title that is equal to my liege's, I have the option to remain as his vassal while in foreign relations, we would be seen as equals.
Well-known example: William as Duke of Normandy and King of England
2 - As a king, I have the option to create a composite monarchy, where I govern my territories as if they were separate kingdoms, and they will be seen on the map as the "Crown of (name of Primary Kingdom)." My prestige gain will be similar to an emperor despite being a king.
Well-known examples: Crown of Aragon, Crown of Castile.
languid ocean