pocketmine\item\Item::addEnchantment PHP Method

    public function addEnchantment(Enchantment $ench)
    {
        if (!$this->hasCompoundTag()) {
            $tag = new CompoundTag("", []);
        } else {
            $tag = $this->getNamedTag();
        }
        if (!isset($tag->ench)) {
            $tag->ench = new ListTag("ench", []);
            $tag->ench->setTagType(NBT::TAG_Compound);
        }
        $found = false;
        foreach ($tag->ench as $k => $entry) {
            if ($entry["id"] === $ench->getId()) {
                $tag->ench->{$k} = new CompoundTag("", ["id" => new ShortTag("id", $ench->getId()), "lvl" => new ShortTag("lvl", $ench->getLevel())]);
                $found = true;
                break;
            }
        }
        if (!$found) {
            $count = 0;
            foreach ($tag->ench as $key => $value) {
                if (is_numeric($key)) {
                    $count++;
                }
            }
            $tag->ench->{$count + 1} = new CompoundTag("", ["id" => new ShortTag("id", $ench->getId()), "lvl" => new ShortTag("lvl", $ench->getLevel())]);
        }
        $this->setNamedTag($tag);
    }