protected function getSortTokens(PlFilter $uf) { if (UserFilter::isGrade($this->grade)) { $sub = $uf->addEducationFilter(true, $this->grade); return 'pe' . $sub . '.' . UserFilter::promoYear($this->grade); } else { $sub = $uf->addDisplayFilter(); return 'pd' . $sub . '.promo'; } }