def colophon(wobj)
      s = @epub.colophon
      if !s.nil? && !wobj.nil?
        wobj.puts s
      end
    end
def colophon(wobj)
      s = @epub.colophon
      if !s.nil? && !wobj.nil?
        wobj.puts s
      end
    end
Write colophon file to IO object +wobj+.