EntityReferenceItemInterface.php

<?php

namespace Drupal\Core\Field\Plugin\Field\FieldType;

use Drupal\Core\Field\FieldDefinitionInterface;

/**
 * Interface definition for field items referencing other entities.
 *
 * Field items should extend \Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItemBase.
 */
interface EntityReferenceItemInterface {
    
    /**
     * Returns the referenceable entity types and bundles.
     *
     * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
     *   The field definition for which to retrieve the referenceable entity
     *   types and bundles.
     *
     * @return array
     *   An array of referenceable bundles where the array is keyed by the entity
     *   type ID, with values an array of bundle names. (It is a single-value
     *   array with the entity type ID if the entity type does not implement
     *   bundles.)
     */
    public static function getReferenceableBundles(FieldDefinitionInterface $field_definition) : array;

}