String types

A string type is a regular expression defining a set of Unicode text strings:

  stringtypeexp  ->  <Sequence> stringtypeexp* </Sequence> |
                     <Optional> stringtypeexp </Optional> |
                     <ZeroOrMore> stringtypeexp </ZeroOrMore> |
                     <OneOrMore> stringtypeexp </OneOrMore> |
                     <Union> stringtypeexp* </Union> |
                     <Intersection> stringtypeexp* </Intersection> |
                     <Complement> stringtypeexp </Complement> |
                     <Repeat Value="..."> stringtypeexp </Repeat> |
                     <Empty/> |
                     <String Value="..."/> |
                     <CharSet Value="..."/> |
                     <CharRange Start=".." End=".."/> |
                     <AnyChar/>

String types are used to specify both valid attribute values and valid character data.

All reasonable data types can be specified using regular expressions. A few examples:

time and date formats
URI syntax
social security numbers
email addresses
ISBN numbers