Issue #3270227 by RenatoG: Implement the bulk operation on add attributes...

      ],

    ];

    // Default field type for attributes.

    $field_type_attributes = 'textarea';

    // Default value for maxlength on attributes.

    $maxlength_attributes = FALSE;

    // Get the field type for attributes.

    if (!empty($config->get('field_type_attributes'))) {

      $field_type_attributes = $config->get('field_type_attributes');

    }

    // Get maxlength if exists.

    if (!empty($config->get('maxlength_attributes'))) {

      $maxlength_attributes = $config->get('maxlength_attributes');

    }

    $form['attributes_to_be_added'] = [

      '#title' => $this->t("Attributes to be added"),

      '#type' => 'textarea',

      '#type' => $field_type_attributes,

      '#description' => $this->t('Here you can insert any attributes, use one per line. For example: data-block-type|info'),

      '#maxlength' => $maxlength_attributes,

      '#states' => [

        'visible' => [

          ':input[name="operation"]' => [