Some sources say there was some sort of law against kingdoms, except for the Kingdom of Bohemia, in the Holy Roman Empire.
Does any expert on the Holy Roman Empire know if that is correct.
Obviously incorrect as the Holy Roman Empire also contained the Kingdoms of Germany, Italy, Hungary, and "Kingdoms" like Burgundy and Lombardy, etc.
So here is what they meant: The Holy Roman Emperor (German Kaiser) ALSO held all those titles, being crowned "King of the Germans" with one crown in Aachen, then "King of the Lombards" in Pavia with the iron crown.. etc. The exception was the Czech King. He was a different dude--not the Kaiser. So while the King of Hungary was ALSO a German emperor, the King of Bohemia was under him. Like any other count or duke, etc.
If you really wanna get a hang of this stuff, I do history podcasts about exactly this. http://bohemican.com for Czech(Bohemian) history, and the History of Germany Podcast for German history (Holy Roman Empire)