What are the formal requirements for being a Holy Roman Emperor and how were they codified? Did they have to be lord of a territory that is part of the HRE?
I imagine they have to be Christians, but do they have to swear spiritual loyalty to the Vatican?
I am particularly interested in these requirements around the time of the 30YW.
Thanks in advance!
Heraldica.org, one of my favourite websites, has a good amount of information for this. Sources are included at the bottom of the page: http://www.heraldica.org/topics/national/hre.htm#Qualifications
The emperor had to be a "worthy" nobleman living within the empire with four noble grandparents. It seems that having territory within the empire was just as good as living it, given the examples of the eligibility of a king of France to be emperor (Alsace), and the retention of the county of Falkenstein by the Duke of Lorraine to be eligible for election.