    # File lib/gettext/tools/pomessage.rb, line 90
        def to_po_str
          raise "msgid is nil." unless @msgid
          raise "sources is nil." unless @sources

          str = ""
          # extracted comments
          if comment
            comment.split("\n").each do |comment_line|
              str << "\n#. #{comment_line.strip}"
            end
          end

          # references
          curr_pos = @@max_line_length
          sources.each do |e|
            if curr_pos + e.size > @@max_line_length
              str << "\n#:"
              curr_pos = 3
            else
              curr_pos += (e.size + 1)
            end
            str << " " << e
          end

          # msgctxt, msgid, msgstr
          str << "\nmsgctxt \"" << msgctxt << "\"" if msgctxt?
          str << "\nmsgid \"" << escaped(:msgid) << "\"\n"
          if plural?
            str << "msgid_plural \"" << escaped(:msgid_plural) << "\"\n"
            str << "msgstr[0] \"\"\n"
            str << "msgstr[1] \"\"\n"
          else
            str << "msgstr \"\"\n"
          end
          str
        end