Rights Expression Language
A Rights Expression Language or REL is a machine-processable language used to express copyright or similar status of data (metadata usable for search, compatibility tracking or DRM).
Most REL are expressible in XML, but this is not a requirement and any format could be used. Some use RDF and RDF Schema. Although RELs may be processed directly, they will most commonly be encountered when embedded as metadata within other documents, such as eBooks, image, audio or video files.