The W3C Publishing Working Group has published a First Public Working Draft on Publication Manifest today. This specification defines a general manifest format for expressing information about a digital publication. It uses schema.org metadata augmented to include various structural properties about publications, serialized in JSON-LD, to enable interoperability between publishing formats while accommodating variances in the information that needs to be expressed.
This manifest format had originally been developed as part of larger work on Web Publications. As a result of some recent discussions, the publication schedule of the group has been modified and, while the Web Publication has been published as a Working Group Note, the Publication Manifest has become a stand-alone, recommendation track document. See a separate blog by Wendy Reid on the backgrounds of this decision.