(*UTF8) - Enables utf8 instead of ascii regular expression.
/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.
(?R) -> .*\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) (?R)
define (DEFINE).
List of differences between .NET and PRCE https://stackoverflow.com/questions/3417644/translate-perl-regular-expressions-to-net