Kinda explained in the title. Say a character has 10 hp max, takes 6 points of damage (Current now 4hp). Then is healed for 7 damage. Using the +/- option on the token bubbles, this would make the Current 11 out of 10, and cause the red bar to "overflow". I've been away from Roll20 for awhile and was trying to setup my APIs again and can't remember what the API I used was called.