A multi-file package is less convenient to create than a single-file package, but it offers more features: it can include multiple Emacs Lisp files, an Info manual, and other file types (such as images).
Prior to installation, a multi-file package is stored in a package archive as a tar file. The tar file must be named name-version.tar, where name is the package name and version is the version number. Its contents, once extracted, must all appear in a directory named name-version, the content directory (see Packaging Basics). Files may also extract into subdirectories of the content directory.
One of the files in the content directory must be named
name-pkg.el. It must contain a single Lisp form,
consisting of a call to the function define-package, described
below. This defines the package's attributes: version, brief
description, and requirements.
For example, if we distribute version 1.3 of the superfrobnicator as a multi-file package, the tar file would be superfrobnicator-1.3.tar. Its contents would extract into the directory superfrobnicator-1.3, and one of these would be the file superfrobnicator-pkg.el.
This function defines a package. name is the package name, a string. version is the version, as a string of a form that can be understood by the function
version-to-list. docstring is the brief description.requirements is a list of required packages and their versions. Each element in this list should have the form
(dep-name dep-version), where dep-name is a symbol whose name is the dependency's package name, and dep-version is the dependency's version (a string).
If the content directory contains a file named README, this file is used as the long description.
If the content directory contains a file named dir, this is
assumed to be an Info directory file made with install-info.
See Invoking install-info. The relevant Info files should also
be present in the content directory. In this case, Emacs will
automatically add the content directory to Info-directory-list
when the package is activated.
Do not include any .elc files in the package. Those are created when the package is installed. Note that there is no way to control the order in which files are byte-compiled.
Do not include any file named name-autoloads.el. This file is reserved for the package's autoload definitions (see Packaging Basics). It is created automatically when the package is installed, by searching all the Lisp files in the package for autoload magic comments.
If the multi-file package contains auxiliary data files (such as
images), the package's Lisp code can refer to these files via the
variable load-file-name (see Loading). Here is an example:
(defconst superfrobnicator-base (file-name-directory load-file-name))
(defun superfrobnicator-fetch-image (file)
(expand-file-name file superfrobnicator-base))