regex
Purpose
Extracts a substring from the input string and formats the extracted substring as specified by regular expression.
Arguments
The first argument is an input string (reference to a named group or a constant) to be modified.
The second argument <regex> is a regular expression that specifies what substring to extract from the input string.
The third argument <format_regex> is a regular expression that specifies how to format the extracted substring. If the argument is omitted, the extracted substring is output as is.