PlayerExpChangeEvent

Called when a players experience changes naturally

当玩家经验值自然变化时触发。

译注：当玩家死亡掉落经验时或使用指令改变经验时都不会触发此事件。只有玩家捡起经验球时才会触发。

Get the amount of experience the player will receive

@return The amount of experience

该方法用于获取玩家经验值的增量。

@return 经验值的增量。

Set the amount of experience the player will receive

@param amount The amount of experience to set

该方法用于设置玩家经验值的增量。

@param amount 经验值的增量。