Link to iarmorvanishable
Used to denote armor items that can have the vanishing enchantment applied.
Link to импорт-класса
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.
Link to implemented-interfaces
IArmorVanishable implements the following interfaces. That means all methods defined in these interfaces are also available in IArmorVanishable