interface PluginFormInterface

interface PluginFormInterface {
    
    /**
     * Form constructor.
     *
     * Plugin forms are embedded in other forms. In order to know where the plugin
     * form is located in the parent form, #parents and #array_parents must be
     * known, but these are not available during the initial build phase. In order
     * to have these properties available when building the plugin form's
     * elements, let this method return a form element that has a #process
     * callback and build the rest of the form in the callback. By the time the
     * callback is executed, the element's #parents and #array_parents properties
     * will have been set by the form API. For more documentation on #parents and
     * #array_parents, see \Drupal\Core\Render\Element\FormElementBase.
     *
     * @param array $form
     *   An associative array containing the initial structure of the plugin form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form. Calling code should pass on a subform
     *   state created through
     *   \Drupal\Core\Form\SubformState::createForSubform().
     *
     * @return array
     *   The form structure.
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state);
    
    /**
     * Form validation handler.
     *
     * @param array $form
     *   An associative array containing the structure of the plugin form as built
     *   by static::buildConfigurationForm().
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form. Calling code should pass on a subform
     *   state created through
     *   \Drupal\Core\Form\SubformState::createForSubform().
     */
    public function validateConfigurationForm(array &$form, FormStateInterface $form_state);
    
    /**
     * Form submission handler.
     *
     * @param array $form
     *   An associative array containing the structure of the plugin form as built
     *   by static::buildConfigurationForm().
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form. Calling code should pass on a subform
     *   state created through
     *   \Drupal\Core\Form\SubformState::createForSubform().
     */
    public function submitConfigurationForm(array &$form, FormStateInterface $form_state);

}