public function referToChild() { return static::foo(); } // Refers to extending foo() method
public function referToParent() { return self::foo(); } // Refers to current/parent class method

$this->form = $this->app->bound('former.form') ? $this->app['former.form'] : null;

abstract class Field extends FormerObject implements FieldInterface
(...)
public function __call($method, $parameters)
    (...)
    if (method_exists($this->group, $method) or Str::startsWith($method, 'onGroup')) {
        (...)
        $method = str_replace('onGroup', '', $method);
        $method = lcfirst($method);
        call_user_func_array(array($this->group, $method), $parameters);
    // (else)
    parent::__call($method, $parameters);