Meta Characters : pattern « XML Schema « XML Tutorial

Meta character  Use/Meaning
.               Match any character, except end-of-line (#x0D and/or #x0A) - same as [^\n\r] 
\               Begin escape sequence
?               Zero or one occurrences
*               Zero or more occurrences
+               One or more occurrences
{ }           Enclose a numeric quantifier or character group
( )           Enclose a regular expression (may be the atom of another regex)
[ ]           Enclose a character class expression

3.79.1.Pattern syntax
3.79.2.list of atoms that match a single character
3.79.3.Character classes
3.79.4.Unicode character classes
3.79.5.User-defined character classes
3.79.6.Meta Characters
3.79.7.These three characters should be used with caution:
3.79.8.A character class expression is simply a character group, enclosed in square brackets
3.79.9.Any single normal character will match only that character
3.79.10.Special regex characters (-[]) cannot be used for the single normal character form of the character range.
3.79.11.Any ASCII letter: adding a second character range to the character group expression
3.79.12.To match a string of any length (including the empty string) that is comprised exclusively of lower-case ASCII letters
3.79.13.Specifying a Pattern for a Simple Type
3.79.14.Pattern for time
3.79.15.You can use patterns to offer choices for an element's content.
3.79.16.Getting rid of leading zeros
3.79.17.Use quantifiers to limit the number of leading zeros-for instance
3.79.18.Merge our three patterns into one
3.79.19.pattern Constrains the lexical space to literals that must match a defined pattern
3.79.20.A phone number
3.79.21.Define a pattern that can be used for zip codes
3.79.22.pattern: USA_SSN datatype