And for those looking for an extended Regexper site that also handles the mentioned (?i) flag
and some other specialities like
named capture groups ^\d(?<groupname>[a-zA-Z])$
or
positive lookbehind assertions (?<=([abc]))
or
negative lookbehind assertions (?<!([abc]))
I found this extended Regexper online site (an extended "clone"):
Source Code on Github
Just switch to the PHP flavour to see the extended possibilities:
