Read more about .NET regular expressions:
http://regexhero.net/reference/
https://msdn.microsoft.com/en-us/library/hs600312%28v=vs.110%29.aspx
https://msdn.microsoft.com/en-us/library/az24scfc%28v=vs.110%29.aspx
http://www.regular-expressions.info/dotnet.html
.NET does not use a /pattern/modifier syntax, but AdiIRC tries to interpret it and remove them from the pattern.
/g /G - Enables global match.
/i /I - Enables case in-sensitive.
/S - Strips any control codes before matching.
/s - Enables single line match.
/m /M /c /C - Enables multi line match.
/x /X - Eliminates unescaped white space from the pattern.
/U - Enables non greedy mode. (Tries to replace greedy patterns with non greedy patterns + > +?, * -> *?)
AdiIRC translate some patterns from PRCE into .NET patterns.
(*UTF8)/(*UTF) -> Enables utf8 instead of ASCII regular expression.\K is not available in .NET, use (<=abc)d instead.
These are not available and have no .NET counterpart:
code (?{…})
recursive (R), (R1), (R&name)
define (DEFINE).
List of differences between .NET and PRCE https://stackoverflow.com/questions/3417644/translate-perl-regular-expressions-to-net