# File scripts/parsing-rules.rb, line 212
    def to_s
      s = super
      s += "\n plus these substitutions:\n" if not subst_rules.empty?
      subst_rules.each do |field, rep_with|
        rep, with = rep_with
        s += "   replace '#{rep.inspect}' in #{field} with '#{with}'\n"
      end
      return s
    end