Other author here... There is this new W3C initiative: <a href="https:&#x2F;&#x2F;www.w3.org&#x2F;community&#x2F;schema-course-extend&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.w3.org&#x2F;community&#x2F;schema-course-extend&#x2F;</a>