r{n1,n2}                  Repeat Operator

    At least n1 and up to n2 repetitions of expression r

         n1, n2 integers with 1 <= n1 <= n2
         r{2,6} ==> rrr?r?r?r?
         r{3,3} ==> rrr
         Expressions grouped by ", (), [], or names, "{name}"
         repeated as a group: (Note the treatment of quoted expressions)
         (r){2,6} ==> (r)(r)(r)?(r)?(r)?(r)?
         [r]{2,6} ==> [r][r][r]?[r]?[r]?[r]?
         {r}{2,6} ==> {r}{r}{r}?{r}?{r}?{r}?
         "r"{2,6} ==> "rr(r)?(r)?(r)?(r)?"