What would be a regex that matches "nl" OR "fr" (without the quotes) but nothing else, case insensitive?
                +3 
                A: 
                
                
              
            Give this a try:
^(nl|fr)$
And use the case insensitive flag.
And I assume you meant nl or fr, and not nlfr.
                  jasonbar
                   2010-03-09 14:42:33
                
              
                +3 
                A: 
                
                
              Alternatives in regular expressions are expressed as expressions separated by the | character.
nl|fr
Case-insensitivity is specified in different ways, in different languages. One way that will work everywhere is to be explicit.
[nN][lL]|[fF][rR]
If you want "the whole string" to be one of those two phrases, then you must anchor it.
^([nN][lL]|[fF][rR])$
                  Jonathan Feinberg
                   2010-03-09 14:43:39
                
              [nN][lL]|[fF][rR], dude that's sick! +1 anyway :)
                  Diadistis
                   2010-03-09 14:46:23
                
                +2 
                A: 
                
                
              
            with regex, (i for case-insensitive)
/^(nl|fr)$/i 
without regex, in your favourite language, just use the equality operator
mystring == "nl" or mystring == "fr"
                  ghostdog74
                   2010-03-09 15:22:36