Adds a specific value validation to Webform

MY_MODULE.module.php

<?php

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * Adds specific value requirement form elements.
 */
function etbu_core_form_alter(&$form, FormState $form_state, $form_id) {
  // Only alter webform UI element forms.
  if ($form_id === 'webform_ui_element_form') {
    $element_properties = $form_state->get('element_properties');

    $form['properties']['validation']['required_value_container'] = [
      '#type' => 'container',
      'required_value_check' => [
        '#type' => 'checkbox',
        '#title' => t('Require specific value?'),
        '#description' => t('If set, this message will be used when a required webform element is empty.'),
        '#default_value' => $element_properties['required_value_check'],
        '#parents' => [
          'properties',
          'required_value_check',
        ],
      ],
      'required_value' => [
        '#type' => 'textfield',
        '#title' => t('Required value'),
        '#description' => t('The value to validate against.'),
        '#default_value' => $element_properties['required_value'],
        '#parents' => [
          'properties',
          'required_value',
        ],
        '#states' => [
          'visible' => [
            ':input[name="properties[required_value_check]"]' => ['checked' => TRUE],
          ],
        ],
      ],
      'required_value_error' => [
        '#type' => 'textfield',
        '#title' => t('Required value error message'),
        '#description' => t('If set, this message will be used when a the webform element does not have the required value.'),
        '#default_value' => $element_properties['required_value_error'],
        '#parents' => [
          'properties',
          'required_value_error',
        ],
        '#states' => [
          'visible' => [
            ':input[name="properties[required_value_check]"]' => ['checked' => TRUE],
          ],
        ],
      ],
    ];
  }
}

/**
 * Implements hook_webform_element_alter().
 *
 * Attaches the validator for specific value requirements.
 */
function etbu_core_webform_element_alter(array &$element, FormStateInterface $form_state, array $context) {
  // Check for desired element.
  if (isset($element['#required_value_check']) && $element['#required_value_check'] == '1' && $element['#required_value'] != "") {
    $element['#element_validate'][] = [
      'Drupal\etbu_core\Validate\WebformRequiredValue',
      'validate',
    ];
  }
}

WebformRequiredValue.php

<?php

namespace Drupal\MY_MODULE\Validate;

use Drupal\Core\Form\FormStateInterface;

/**
 * Form API callback. Validate element value.
 */
class WebformRequiredValue {
  /**
   * Validates given element.
   */
  public static function validate(array &$element, FormStateInterface $formState, array &$form) {
    $webformKey = $element['#webform_key'];
    $value = $formState->getValue($webformKey);
    $requiredValue = $element['#required_value'];

    if ($value != $requiredValue) {
      if (isset($element['#required_value_error']) && $element['#required_value_error'] != "") {
        $formState->setError($element, $element['#required_value_error']);
      }
      else {
        $tArgs = [
          '%name' => empty($element['#title']) ? $element['#parents'][0] : $element['#title'],
          '%value' => $value,
        ];
        $formState->setError(
          $element,
          t('%value is not the required value for the field %name. Please use a different value.', $tArgs)
        );
      }
    }
  }

}