# File lib_wpm/wpm.rb, line 971
    def expand_string_key(value)
      src_list = value.scan(/\$|[^\$]+/)
      dst = ''
      while (fragment = src_list.shift)
        if (fragment == '$') then
          if (src_list.empty?) then
            dst.concat(fragment)
          else
            next_fragment = src_list.shift
            if (next_fragment == '$') then
              dst.concat('$')
            elsif (next_fragment =~ /^\{(.*?)\}/) then
              key = $1
              following = $'
              dst.concat(expand_string(key))
              dst.concat(following)
            else
              dst.concat(fragment)
              dst.concat(next_fragment)
            end
          end
        else
          dst.concat(fragment)
        end
      end

      dst
    end