The Find First Character That Does Not Occur in Set routine
    searches a string, comparing each character to the characters in
    a specified set of characters. The string is searched character
    by character, from left to right. STR$FIND_FIRST_NOT_IN_SET
    returns the position of the first character in the string that
    does not match any of the characters in the selected set of
    characters.

    Format

      STR$FIND_FIRST_NOT_IN_SET  source-string ,set-of-characters