A developer preview release is a release of all, or part, of the final package meant to be tested by potential early-adopters. It is meant to garner feedback on existing functionality, missing functionality, unexpected use-cases, etc. Testers are expected to have a high degree of proficiency with metadata, Java, and Javdoc, and be willing to develop a basic understanding of Spring.
A developer preview release is not a final set of APIs. Any API may change, perhaps drastically, between releases.
All feedback should be sent to the developers mailing list. If, after discussion, the topic initiator is asked to submit an issue for the topic then the issue should be filed with the metadata aggregator project.
Use in Production
A developer preview release should never be used in a production environment.