core + pending (Pending Extension): these terms are pending wider review. Feedback is welcomed!

previewUrl

Defined in the pending.schema.org extension.
Canonical URL: http://schema.org/previewUrl

Thing > Property > previewUrl

A link to a site where a preview of the course is offered.

Usage: Between 100 and 1000 domains
Values expected to be one of these types
URL
Used on these types
Course

Source

https://github.com/schemaorg/schemaorg/issues/195

Schema Version 3.1