There are conventions for writing minor modes just as there are for major modes. Several of the major mode conventions apply to minor modes as well: those regarding the name of the mode initialization function, the names of global symbols, the use of a hook at the end of the initialization function, and the use of keymaps and other tables.
In addition, there are several conventions that are specific to
minor modes. (The easiest way to follow all the conventions is to use
define-minor-mode; Defining Minor Modes.)
nilto disable; anything else to enable).
If possible, implement the mode so that setting the variable automatically enables or disables the mode. Then the minor mode command does not need to do anything except set the variable.
This variable is used in conjunction with the
display the minor mode name in the mode line. It can also enable
or disable a minor mode keymap. Individual commands or hooks can also
check the variable's value.
If you want the minor mode to be enabled separately in each buffer, make the variable buffer-local.
The command should accept one optional argument. If the argument is
nil, it should toggle the mode (turn it on if it is off, and
off if it is on). It should turn the mode on if the argument is a
positive integer, the symbol
t, or a list whose car is one
of those. It should turn the mode off if the argument is a negative
integer or zero, the symbol
-, or a list whose car is a
negative integer or zero. The meaning of other arguments is not
Here is an example taken from the definition of
It shows the use of
transient-mark-mode as a variable that enables or
disables the mode's behavior, and also shows the proper way to toggle,
enable or disable the minor mode based on the raw prefix argument value.
(setq transient-mark-mode (if (null arg) (not transient-mark-mode) (> (prefix-numeric-value arg) 0)))
minor-mode-alistfor each minor mode (see Definition of minor-mode-alist), if you want to indicate the minor mode in the mode line. This element should be a list of the following form:
Here mode-variable is the variable that controls enabling of the minor mode, and string is a short string, starting with a space, to represent the mode in the mode line. These strings must be short so that there is room for several of them at once.
When you add an element to
check for an existing element, to avoid duplication. For example:
(unless (assq 'leif-mode minor-mode-alist) (setq minor-mode-alist (cons '(leif-mode " Leif") minor-mode-alist)))
or like this, using
add-to-list (see List Variables):
(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
Global minor modes distributed with Emacs should if possible support
enabling and disabling via Custom (see Customization). To do this,
the first step is to define the mode variable with
If just setting the variable is not sufficient to enable the mode, you
should also specify a
:set method which enables the mode by
invoking the mode command. Note in the variable's documentation string that
setting the variable other than via Custom may not take effect.
Also mark the definition with an autoload cookie (see autoload cookie),
and specify a
:require so that customizing the variable will load
the library that defines the mode. This will copy suitable definitions
into loaddefs.el so that users can use
enable the mode. For example:
;;;###autoload (defcustom msb-mode nil "Toggle msb-mode. Setting this variable directly does not take effect; use either \\[customize] or the function `msb-mode'." :set 'custom-set-minor-mode :initialize 'custom-initialize-default :version "20.4" :type 'boolean :group 'msb :require 'msb)blog comments powered by Disqus