Patterns — regular expression patterns
Patterns in configuration parameters and expressions use the standard Java regular expression Pattern class. For more information on regular expressions, see Oracle's tutorial on Regular Expressions.
A regular expression pattern template expresses a transformation to be
applied 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.