What exactly do you want to accomplish? Create a flowable BPMN diagram? Why not use the flowable on board facilities for it?
If you want to support a custom vendor extensions you can use any elements to create them:
moddle.createAny('eventType', 'http://flowable.org/bpmn', {
$body: '<![CDATA[lll]]>'
});
Alternatively you create a custom moddle schema for it.