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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.^[1] Although the exact syntax used for regular expressions varies from one technology to the next, the fundamentals are the same.^[2]

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. ...