See bpmn-elements for supported elements. The engine only support elements and attributes included in the BPMN 2.0 scheme, but can be extended to understand other schemas and elements.
The aim is to, at least, have BPMN 2.0 core support.
The module uses debug so run with environment variable
DEBUG=bpmn-engine:* or provide your own logger.
A pretty image of a process
The bpmn-engine resides upon the excellent library bpmn-io/bpmn-moddle developed by bpmn.io
One excellent modeller is the Camunda modeler.