Appendix B. XML Schema Regular Expressions
A regular expression is a kind of mini programming language used for text pattern matching. Regular expressions have been around for a long time and are supported by many different tools and programming languages, including Java, Perl, Python, sed, awk, procmail, grep, vi, and emacs, to name a few. Although the exact syntax used for regular expressions varies from one technology to the next, the fundamentals are the same.
In XML schemas, regular expressions are used with the pattern facet to restrict the values allowed for a derived simple type. Regular expressions tell us which characters can be used for a simple type value.
For example, we can decide that a phone number should contain only digits. ...