XML Schema Complete Reference, The

14.2. Regular Expression Syntax

A regular expression is a set of characters that represents a pattern. Many instance strings may match the pattern identified by the regular expression. Any set of characters in a regular expression may be required, repeated, optional, or otherwise controlled. Because of this flexibility, the number of strings that match a regular expression is potentially unbounded.

14.2.1. Metacharacters

A regular expression has a number of special characters, or metacharacters, that generally denote groupings or repetition. Table 14.1 describes these metacharacters.

Table 14.1. Metacharacter Examples

Metacharacter	Description	Sample Regular Expression	Match Sample
.	Match any character as defined by The Unicode Standard.