### Matching Rules for Extended Regular Expressions

The following rules apply within an Extended Regular Expression:

- An ordinary character matches itself. The simplest form of regular expression is a string of characters with no special meaning.
- A special character preceded by a backslash matches itself. The special characters are:

         . [ \ * ^ $ ( ) + ? { |

- A period (.) without a backslash matches any character except the null character.
- An expression within square brackets ( [ ] ), a bracket expression, matches a single character or collating element.

Regular Expressions

Additional Syntax Specifiers for Extended Regular Expressions