With this data pack, a player can be set in UHC Mode (No natural regeneration) without applying the rule to the entire server.
This is useful if a player want's a challenge or to do special events for a group of players.
When the data pack is first loaded, players get a book where they can select which mode they will be playing.
Players can also get a book by activating a trigger using this command:
/trigger get_uhc_info set 1