The event is not cancelable.

The event does not have a result.

Importare la Classe

Link to importare-la-classe

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.

import crafttweaker.api.event.entity.player.xp.MCPlayerXPEvent;

Extending MCPlayerEvent

Link to extending-mcplayerevent

MCPlayerXPEvent extends MCPlayerEvent. That means all methods available in MCPlayerEvent are also available in MCPlayerXPEvent