- https://www.php.net/manual/en/book.pcre.php
- https://www.php.net/manual/en/reference.pcre.pattern.syntax.php
- https://php.watch/articles/php-regex-readability
- https://regex101.com/
- https://www.rexegg.com/regex-php.php
- https://www.phpliveregex.com/
- https://www.pcre.org/current/doc/html/
- https://pcre2project.github.io/pcre2/
- https://www.pcre.org/
- https://github.com/PCRE2Project/pcre2
- https://www.regular-expressions.info/php.html
- https://github.com/PCRE2Project/pcre2/blob/master/NEWS
- https://github.com/PCRE2Project/pcre2/blob/master/ChangeLog
- https://github.com/PCRE2Project/pcre2/releases
Note that since PHP 7.3.0, PHP's RegEx implementation uses PCRE2 (aka: >=PCRE 10.00).