public FormBuilder::rebuildForm($form_id, FormStateInterface &$form_state

public FormValidatorInterface::validateForm($form_id,

public FormStateDecoratorBase::setMethod($method)

public static SubformState::createForSubform(array &$subform, array &$parent_form

protected SubformState::__construct(array &$subform, array &$parent_form

Similar to self::$build_info, but pertaining to

public FormAjaxSubscriber::onView(GetResponse

protected FormBase::config($name) Retrieves

public FormStateInterface::setErrorByName($name, $message = '')

public static FormStateInterface::hasAnyErrors()