code: protected function country()
      {
          $this->parts['{country}'] = $this->form->field($this->model, $this->model->getCountryPropertyName(), ['options' => ['class' => 'form-group']])->dropDownList(
                  ArrayHelper::map(Country::find()->orderBy(['name' => SORT_ASC])->all(), 'id', 'name'), [
              'id' => $this->fieldIds['country']
              , 'prompt' => Yii::t('jlorente/location', 'Select country')
              , 'name' => $this->getSubmitModelName($this->model->getCountryPropertyName())
          ]);
      }
docs: Renders the country part.