'New Architect' (what used to be called 'Web Technique) has a good overview of Digital Rights Management (DRM) technology in their current issue. For good or for worse, DRM is here to stay and we may as well familiarize ourselves with the technology. The standards in the Rights Expressions languages seem to have a long way to go. XrML, being pushed by ContentGuard (a Microsoft venture) is best positioned (of course!) and apparently the most matured of the lot. The other biggies are also backing XMCL - a competitive move by RealNetworks.

Also check out the XHTML Guidelines from NYPL (via A list apart).