With the exception of open content in several places, this specification has omitted extensibility. Extensibility can help with the development of future versions of the specification and possible extensions.

Notes
Vivian: JSTL, tacked on an open ended datatype for every entity. Allow free content (at your own risk). SAF uses extensibility for Protocol.Process, Symptom.Content, etc. Allows extensibility for Practitioner, Symptoms Emitter. But energy domain consumers (for example) may need additional fields that we haven't considered. Use at your own risk