[]=

# File actionpack/lib/action_dispatch/journey/gtg/transition_table.rb, line 168
        def []=(from, to, sym)
          case sym
          when String, Symbol
            to_mapping = @string_states[from] ||= {}
            # account for symbols in the constraints the same as strings
            to_mapping[sym.to_s] = to
          when Regexp
            if sym == DEFAULT_EXP
              @stdparam_states[from] = to
            else
              to_mapping = @regexp_states[from] ||= {}
              # we must match the whole string to a token boundary
              to_mapping[/\A#{sym}\Z/] = to
            end
          else
            raise ArgumentError, "unknown symbol: %s" % sym.class
          end
        end