How to add another checkbox like `Required` for the question element. about angular-surveys HOT 1 OPEN

<div layout="row" layout-align="start center">
                <div flex="20">
                    <md-button class="md-accent md-raised" type="button" role="button" ng-click="ctrl.save()" translate="mwForm.buttons.questionReady">
                        Ready
                    </md-button>
                </div>
                <div flex>
                    <md-checkbox  ng-model="ctrl.question.required" ng-disabled="ctrl.readOnly" flex>
                        <span translate="mwForm.question.required">Required</span>
                    </md-checkbox>
                    <md-checkbox  ng-model="ctrl.question.calc" flex>
                        <span>New CheckBox</span>
                    </md-checkbox>
                </div>