>>You might want to be careful with this if there is a possiblity of Asian-language text (e.g. Chinese, Japanese, Korean) which use double-byte character sequences.
>>
>>You probably also want to include the chr(9) (horizontal tab) as one of the valid characters.
>
>Asian or other non US character data will not be an issue here (at least not in the forseeable future).

The easiest way to automatically expand the list of characters is to go from 128 to 255, and if isalpha(n), include it - it is a character in the current codepage. You only need to recompile the app in a specific codepage (see set cpcompile) for this to work. I've tried it with Serbian diacritical characters, with Cyrillic too, and it works - actually I can have variables with any characters which are allowed in the current set("cpcompile"). If I wanted, I could have all my variables, names of functions, prg files etc in Cyrillic :).