Minecraft wiki entry for Item_modifier, associated text: apply_bonus—Applies a predefined bonus formula.
 enchantment: Enchantment ID used for level calculation.
 formula: Can be binomial_with_bonus_count for a binomial distribution (with n=level + extra, p=probability), uniform_bonus_count for uniform distribution (from 0 to level * bonusMultiplier), or ore_drops for a special function used for ore drops in the vanilla game (Count * (max(0; random(0..Level + 2) - 1)+1)).
 parameters: Values required for the formula.
 extra: For formula 'binomial_with_bonus_count', the extra value.
 probability: For formula 'binomial_with_bonus_count', the probability.
 bonusMultiplier: For formula 'uniform_bonus_count', the bonus multiplier.