Unlike regular expressions, pattern matching is case insensitive. To force case sensitivity, you can add the named argument MATCHCASE to either Pat Match() or Regex Match(). For example:
string = "abcABC";
result = Regex Match( string, Pat Regex( "[aBc]+" ) );
Show( string, result );
/ *returns string = "abcABC"
result = {"abcABC"}*/
result = Regex Match( string, Pat Regex( "[cba]+" ), NULL, MATCHCASE );
Show( string, result );
/* returns string = "abcABC"
result = {"abc"}*/