Patterns
Patterns in configuration parameters and expressions use the standard Java regular expression Pattern class. For more information on regular expressions, refer to Oracle’s tutorial on Regular Expressions.
Pattern templates
A regular expression pattern template expresses a transformation to apply for a matching regular expression pattern.
It may contain references to capturing groups
within the match result.
Each occurrence of $g, where g is an integer value, is substituted by the indexed capturing group in a match result.
Capturing group zero "$0" denotes the entire pattern match.
A dollar sign or numeral literal immediately following a capture group reference can be included
as a literal in the template by preceding it with a backslash (\).
Backslash itself must be also escaped in this manner.
More information
Java Pattern class