The interface uses debconf for consistency with the rest of the Debian
installer.

On startup, the tasksel program will read all *.desc files in
/usr/share/tasksel/ for information about what tasks are available. The
tasks will be presented in a simple list selection screen with their short
descriptions.

On exit, tasksel executes the appropriate command to install the selected
packages. If the -t option is given, then tasksel prints out the command
line to use to stdout instead. All other messages are printed to stderr.

To get a new task added, please file a bug report on tasksel.

Debian derived distributions can add a new .desc file to
/usr/share/tasksel/ to add additional tasks, or modify/divert
debian-tasks.desc to remove tasks.

The file format is a rfc-822 style stanza, with fields named Task, Section,
Description (which should include an extended description), Key, Depends, 
and optional Test- and Source fields. Here is an example:

Task: desktop
Section: user
Relevance: 10
Description: Desktop environment
 This task provides basic "desktop" software, including a variety
 of session managers, file managers and web browsers. It incorporates
 both the GNOME and KDE desktops, and provides a display manager
 which lets the user choose between the two.
Key:
  x-window-system-core
  kde
  gnome
Packages: task-fields

The Key field lists packages that are essential to the task. If those
packages are not available, then the task will not be available either. It
need not list all the packages in the task, if some only serve to make it
better when they are available.

The Packages field tells how to get a complete list of packages that are in
the task. In the example above, it uses the task-fields method, which is
built into tasksel, and looks for Task fields in the control data of available
packages, that list the name of the task. It's also possible to define
other methods, by adding programs to /usr/lib/tasksel/packages/. Then
list the name of the program as the value for the task field, and it will
be run and passed the name of the task, and should output a list of
packages in that task.

There is support for automatically installing tasks based on test programs.
If a task has a Test-* field, then a program in /usr/lib/tasksel/tests/
will be run. For example Test-lang fields cause /usr/lib/tasksel/tests/lang
to be run. The test is passed first the name of the tasks, and then the
contents of the field as parameters. The exit code of the test controls
what to do with the task:

0 - do not display, but do install task
1 - do not display task 
2 - display task, marked for installation
3 - display task, not marked for installation

One use of these tests is in automatically selecting a language task
appropriate for the user's locale, and hiding the rest. The lang test
handles this by comparing the value of the Test-lang field of a task with
the locale setting. Tests could also be used for things like automatically
installing hardware support tasks on systems with the right hardware.

There is rudimentary support for tasks that depend on other tasks. If a
task has a Depends field, then it should only be installed if all the tasks
listed as dependencies are installed.

If a task is important enough that it should go near the top of its
section, give it a relevance of 9 or 10. If a task is not likely to be
used, give it a relevance of 1. Default is 5.