Frank, I understand Debian Policy's purpose is to document what Debian considers good practice, not document the tools that may be used. Thus, I think it is perfectly acceptable for Debian Policy to defer to the update-menu documentation for the proper format of the menu files.
If this bug is suggesting that the information should be available somewhere, then the menufile(5) manpage may be useful. However, if you think that Debian Policy is the correct place for the menu file syntax, please followup with reasons why Debian Policy should include it rather than let the update-menu tool's documentation describe its configuration files. (I seem to recall another bug that wanted to move documentation into policy, possibly involving mime-support, but I cannot find it now. It may be useful to discuss both simultaneously.) Thanks. :) -- Earthlink: The #1 provider of unsolicited bulk email to the Internet.