,
Request matching directives use POSIX extended regular expressions by
default. If pound was compiled with PCRE or
PCRE2 library, Perl-compatible regular expressions can be
used instead. This can be done either globally or individually for a
given directive.
To change regular expression type globally, use the following directive:
RegexType pcre
It affects all request matching directives that appear after it in the
configuration file, until next RegexType directive or end of
file, whichever occurs first. To change back to POSIX regular
expressions, use posix argument:
RegexType posix
Argument to the RegexType directive is case-insensitive.
Regular expression type can also be selected individually for a directive, using -posix or -pcre flags. For example:
Host -pcre -icase "(?<!www\\.)example.org"