This is reflected in the in-game book http://www.imperial-library.info/content/skyrims-rule.
The reality, however, is that the High King swears fealty to the Emperor, and as Solitude is the city most directly influenced by Imperial culture and politics, the Jarl of Solitude has served as High King for generations. The Moot, therefore, is more formality and theater than anything else.
But as I prepared to leave Skyrim, I could feel a change in the air, sense the trepidation of some of the good Nord people. Many seemed unhappy with the Empire's continued presence in their land. And the outlawing of the worship of Talos as the Ninth Divine - a stipulation of the White-Gold Concordat, the peace treaty between the Empire and Aldmeri Dominion - has only strengthened that division.
So while the Jarls of Skyrim still control their holds, and those Jarls are ruled over by their Imperial-sanctioned High King, will there come a day when the Moot convenes to select a new High King - one that is not, as many would say, the Emperor's "Solitude puppet"?
If that day comes, I will be thankful to be far away from Skyrim, in my own home of Hammerfell. For such a decision could well mean civil war, and I fear that such a conflict would tear the fierce and beautiful Nord people asunder.

They have no limit on their magicka.