ds-8.x-3.9/tests/modules/ds_test/src/Plugin/DsField/TestMultipleField.php

<?php

namespace Drupal\ds_test\Plugin\DsField;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\ds\Attribute\DsField;
use Drupal\ds\Plugin\DsField\DsFieldBase;

/**
 * Test field plugin.
 */
#[DsField(
  id: 'test_multiple_field',
  title: new TranslatableMarkup('Test multiple field plugin'),
  entity_type: 'node'
)]
class TestMultipleField extends DsFieldBase {

  /**
   * {@inheritdoc}
   */
  public function build() {
    return [
      0 => [
        '#markup' => 'Test row one of multiple field plugin on node ' . $this->entity()->id(),
      ],
      1 => [
        '#markup' => 'Test row two of multiple field plugin on node ' . $this->entity()->id(),
      ],
    ];
  }

  /**
   * {@inheritdoc}
   */
  public function isMultiple() {
    return TRUE;
  }

}