This question already has an answer here: Reference – What does this regex mean? (1 answer) Closed 5 hours ago. ^((?!ca-ct.mydomain)(?!ca.mydomain)(?!cats.mydomain).)*mydomain.com$ I got the above expression from a web.config file, it’s supposed to filter out anything that contains ca-ct.mydomain or ca.mydomain or cats.mydomain I just cannot understand what the .)* piece means, the closing parenthesis […]