D.5 Conventional Headers for Emacs Libraries

Emacs has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. This section explains these conventions.

We'll start with an example, a package that is included in the Emacs distribution.

Parts of this example reflect its status as part of Emacs; for example, the copyright notice lists the Free Software Foundation as the copyright holder, and the copying permission says the file is part of Emacs. When you write a package and post it, the copyright holder would be you (unless your employer claims to own it instead), and you should get the suggested copying permission from the end of the GNU General Public License itself. Don't say your file is part of Emacs if we haven't installed it in Emacs yet!

With that warning out of the way, on to the example:

     ;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers
     
     ;; Copyright (C) 1992 Free Software Foundation, Inc.
     
     ;; Author: Eric S. Raymond <esr@snark.thyrsus.com>
     ;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com>
     ;; Created: 14 Jul 1992
     ;; Version: 1.2
     ;; Keywords: docs
     
     ;; This file is part of GNU Emacs.
     ...
     ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
     ;; Boston, MA 02111-1307, USA.

The very first line should have this format:

     ;;; filename --- description

The description should be complete in one line.

After the copyright notice come several header comment lines, each beginning with ‘;; header-name:’. Here is a table of the conventional possibilities for header-name:

‘Author’

This line states the name and net address of at least the principal author of the library.

If there are multiple authors, you can list them on continuation lines led by ;; and a tab character, like this:

          ;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu>
          ;;      Dave Sill <de5@ornl.gov>
          ;;      Dave Brennan <brennan@hal.com>
          ;;      Eric Raymond <esr@snark.thyrsus.com>
     

‘Maintainer’

This line should contain a single name/address as in the Author line, or an address only, or the string ‘FSF’. If there is no maintainer line, the person(s) in the Author field are presumed to be the maintainers. The example above is mildly bogus because the maintainer line is redundant.

The idea behind the ‘Author’ and ‘Maintainer’ lines is to make possible a Lisp function to “send mail to the maintainer” without having to mine the name out by hand.

Be sure to surround the network address with ‘<...>’ if you include the person's full name as well as the network address.

‘Created’

This optional line gives the original creation date of the file. For historical interest only.

‘Version’

If you wish to record version numbers for the individual Lisp program, put them in this line.

‘Adapted-By’

In this header line, place the name of the person who adapted the library for installation (to make it fit the style conventions, for example).

‘Keywords’

This line lists keywords for the finder-by-keyword help command. Please use that command to see a list of the meaningful keywords.

This field is important; it's how people will find your package when they're looking for things by topic area. To separate the keywords, you can use spaces, commas, or both.

Just about every Lisp library ought to have the ‘Author’ and ‘Keywords’ header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names—they have no standard meanings, so they can't do any harm.

We use additional stylized comments to subdivide the contents of the library file. These should be separated by blank lines from anything else. Here is a table of them:

‘;;; Commentary:’

This begins introductory comments that explain how the library works. It should come right after the copying permissions, terminated by a ‘Change Log’, ‘History’ or ‘Code’ comment line. This text is used by the Finder package, so it should make sense in that context.

‘;;; Documentation’

This has been used in some files in place of ‘;;; Commentary:’, but ‘;;; Commentary:’ is preferred.

‘;;; Change Log:’

This begins change log information stored in the library file (if you store the change history there). For Lisp files distributed with Emacs, the change history is kept in the file ChangeLog and not in the source file at all; these files generally do not have a ‘;;; Change Log:’ line. ‘History’ is an alternative to ‘Change Log’.

‘;;; Code:’

This begins the actual code of the program.

‘;;; filename ends here’

This is the footer line; it appears at the very end of the file. Its purpose is to enable people to detect truncated versions of the file from the lack of a footer line.