pocketmine\item\Item::getModifyAttackDamage PHP Method

    public function getModifyAttackDamage(Entity $target)
    {
        $rec = $this->getAttackDamage();
        $sharpL = $this->getEnchantmentLevel(Enchantment::TYPE_WEAPON_SHARPNESS);
        if ($sharpL > 0) {
            $rec += 0.5 * ($sharpL + 1);
        }
        if ($target instanceof Skeleton or $target instanceof Zombie or $target instanceof Witch or $target instanceof PigZombie) {
            //SMITE    wither skeletons
            $rec += 2.5 * $this->getEnchantmentLevel(Enchantment::TYPE_WEAPON_SMITE);
        } elseif ($target instanceof Spider or $target instanceof CaveSpider or $target instanceof Silverfish) {
            //Bane of Arthropods    wither skeletons
            $rec += 2.5 * $this->getEnchantmentLevel(Enchantment::TYPE_WEAPON_ARTHROPODS);
        }
        return $rec;
    }