the actual change applied - less than delta once clamping bites, and 0 for a
stat already at its cap - so a game can tell "Attack won't go any higher!" from a real
change
a stat's current stage; 0 for one never changed
resets every stage to 0, removing every modifier this applied - the switch-out rule
Raises (or, given a negative
delta, lowers)stat's stage, clamped to ±max.