[dev_slash_null]

Just in case you haven't seen the postmortem of the Cloudflare outage which also was caused by a regex based DoS: https://blog.cloudflare.com/details-of-the-cloudflare-outage...

[radiojosh]

That was a great read, but there was one thing I didn't understand: Why would the regex string have "." twice in a row? What does ".." find that "." doesn't find? Does that just mean "at least two characters"?

[rjbwork]

It means specifically 2 characters, and is equivalent to .{2}

..+ or ...* are ways of writing "at least two characters".

[bn-usd-mistake]

A single `.` matches exactly one character. `..` matches exactly two characters (not more, not less).