regexp2 - full featured regular expressions for Go

Regexp2 is a feature-rich RegExp engine for Go. It doesn't have
constant time guarantees like the built-in regexp package, but it
allows backtracking and is compatible with Perl5 and .NET. You'll
likely be better off with the RE2 engine from the regexp package
and should only use this if you need to write very complex patterns
or require compatibility with .NET.