Minecraft wiki entry for Item_modifier, associated text: looting_enchant—Adjusts the stack size based on the level of the Looting enchantment on the entity that killed the entity triggering this item modifier.
 count: Number provider. Specifies the number of additional items per level of looting. Note the number may be fractional, rounded after multiplying by the looting level.
 limit: Specifies the maximum amount of items in the stack after the looting calculation. If the value is 0, no limit is applied.