Drupal Form Validation

validateForm() Method

public function validateForm(array &$form, FormStateInterface $form_state): void {
  $name = $form_state->getValue('name');

  if (strlen($name) < 3) {
    $form_state->setErrorByName('name', $this->t('Name must be at least 3 characters.'));
  }

  if (!preg_match('/^[a-zA-Z\s]+$/', $name)) {
    $form_state->setErrorByName('name', $this->t('Name may only contain letters and spaces.'));
  }
}

setError vs setErrorByName