Requests for Comments, by the Internet Engineering Task Force of the Internet Society. Base URL http://www.ietf.org/rfc/.
Uniform Resource Identifiers (URI), Generic Syntax, RFC 2396, August 1998, rfc2396.txt
Uniform Resource Locators (URL), RFC 1738, December 1994, rfc1738.txt
URN Namespace Definition Mechanisms, RFC 2611, June 1999, rfc2611.txt
URN Syntax, RFC 2141, May 1997, rfc2141.txt
XML Schema Recommendation, by World Wide Web Consortium. Base URL http://www.w3.org/TR/.
Part 0: Primer, xmlschema-0.html
Part 1: Structures, xmlschema-1.html
Part 2: Datatypes, xmlschema-2.html
XML Schemas: Best Practice Homepage, at Roger Costello's xFront site. Base URL http://www.xfront.org/BestPracticesHomepage.html. This very good site addresses several issues having to do with the W3C XML Schema language. Particularly in regard to this chapter, I recommend the piece on regular expressions as used in the W3C XML Schema language.