If a backend service return an rejected promise, node should not be moved.
Example of usage from an agular directive:
 oc.$chart
 .on('validate.nodedropped.orgchart', event => {
 let defer = $q.defer();
 CustomerHierarchyService
 .moveSection(event.draggedNode[0].id, event.dropZone[0].id)
 .then(() => {
 Message.showSuccess("Section was successfully moved!");
 defer.resolve();
 })
 .catch((error) => {
 Message.showError(error.data.responseStatus.message);
 defer.reject();
 });
 return defer.promise;
 })
 .on('click','.node', function () {
 var $this = $(this);
 $('#selected-node').val($this.find('.title').text()).data('node', $this);
 })
 .on('dblclick','.node', function () {
 editNode($(this));
 })
 .on('click', '.orgchart', event => {
 if (!$(event.target).closest('.node').length) {
 $('#selected-node').val('');
 }
 });