How to add tag on item?

Hi, I was wondering how to add tag to an item... I used

PHP:

 $item->setNamedTag($tag);

But it gave this error

Code:

 pocketmine\item\Item::setNamedTag must be instanceof CompundTag 

Thanks for help

 

use setCustomName()

 

How to add Item in inventory with custom name then?

 

PHP:

$item = Item::DIAMOND_SWORD
$item->setCustomName("hi");
$player->getInventory()->addItem($item);


 

Thanks !