plus-ui/public/static/flowable-modeler/editor-app/configuration/properties/trigger-mode-write-template.html

<div ng-controller="FlowableTriggerModeCtrl">
    <select ng-model="property.value" ng-change="triggerModeChanged()">
    	<option>default</option>
    	<option>onEvent</option>
    </select>
</div>