is a standard defining a format for public key certificates. The standard is well established. It should normally offer interoperability between certificates issued by different certification authorities. Unfortunately it is not fully true. Peter GUTMAN’s x509 guide is a very good presentation of this format.
XrML (eXtended rights Markup Language)
is a language that enables content providers to specify rights and their associated terms and conditions for distributing and using digital contents. For instance for each right there is an associated validity period, a fee, a territory, and access conditions. XEROX developed the initial versions. Now ContentGuard manages the current specifications.