I do not think this is possible. The problem is that the Regex compiles (parses) the pattern so once it's created you would have to reparse it. Theoretically speaking you could add ignoreCase accessors to RxMatcher but it is likely it would break things; or add method to RxMatcher that would return a new RxMatcher object with the proper settings. Also note that regular expressions in Pharo are not the extended versions, where these things are usually available (alongside lookahead/lookbehind and other). And personally I find the Regex library so awkward to use that I always opt for PetitParser. ~~~~ myParser := 'hello' asParser. myParser matches: 'Hello'. "false" myParser caseInsensitive matches: 'Hello'. "true" ~~~~ on the other hand there is no option to turn it back again. So if you regularly need to switch it back and forth it wouldn't be solution either. Peter