$this->validatorSchema['question_2'] = new sfValidatorChoice(array(
                        'multiple' => true,
                        'choices' => array_keys(self::getBusinessEmerge()),
                        'min' => 1,
                        'max' => 3,
                ),array(
                        'required' => 'You must select upto three options'
                ));



At most 3 values must be selected (4 values selected).