http://www.loc.gov/standards/valuelist/rdacontent.html
http://www.loc.gov/standards/valuelist/rdacarrier.html
http://www.loc.gov/standards/valuelist/rdamedia.html
http://www.loc.gov/marc/bibliographic/bd264.html
http://www.loc.gov/marc/changes-rda-336.html
http://www.loc.gov/marc/changes-rda-337.html