public function setAttribute($a, $v)
    {
        parent::setAttribute($a, $v);
        if ($a == 'id') {
            foreach ($this->fieldsets as $i => $fieldset) {
                $id = $v . '-fieldset-' . ($i + 1);
                $fieldset->setAttribute('id', $id);
            }
        } else if ($a == 'class') {
            foreach ($this->fieldsets as $i => $fieldset) {
                $class = $v . '-fieldset';
                $fieldset->setAttribute('class', $class);
            }
        }
        return $this;
    }