It seems that once you have a named capture in a regular expression,  
you can no longer use numeric captures.

          m = /(.)(.)(?<digit_prefix>\d+)(\d)/.match("THX1138.")
          m.begin(:digit_prefix)
          m.begin(2)    #=> index 2 out of matches

         $1 #=>  113
         $2 #=> nil

         m.to_a  #=> => ["HX1138", "113"]


Is this expected?


Dave