Emacs: Major Mode

What is Major Mode

• A major mode is a collection of emacs settings and commands, designed for specific task.
• Each buffer is associated with one major mode, and only one.

Example of major modes:

• programing languages: emacs-lisp-mode, python-mode, js-mode etc.
• dired 〔see Emacs: File Manager, dired〕
• shell 〔see Emacs: Run Shell〕
• image-mode 〔see Emacs: View Image File〕
• eww 〔see Emacs: Eww Web Browser〕

Technical Meaning of Emacs Major Mode

For elisp coders, technically a major mode means:

• A command that initiate the mode, mostly setting many Buffer Local Variable. This command is required.
• The Buffer Local Variable includes syntax table, keymap, abbrev table, font-lock-defaults, etc. Some of these such as syntax table is not technically a buffer local variable, but is a value local for each buffer.
• Many special commands for a specific task the major mode is designed for. E.g. In programing language modes, commands for formatting code etc, or special mode such as dired, Emacs: eshell, Emacs: View Image File, etc.
• And or set up text properties, text overlay, hook, etc.

〔see Elisp: Create Major Mode〕

Switch to a Major Mode

Each major mode has a associated command. e.g. shell, js-mode, python-mode.

The command to turn on a major mode usually ends in “-mode”, but not always.

To switch to a major mode, just Alt+x major_mode_command_name

When you open a file, a chosen major mode is automatically turned on, depending on file name or other ways. 〔see Emacs Init: Set Default Major Mode〕

Find the Name of Current Major-Mode

The current major mode's name is stored in a variable major-mode

major-mode

A Buffer Local Variable . Value is Symbol of current buffer's major mode. 〔see Emacs: Show Variable Value and Doc〕

Major Mode's Display Name

Each major have a display name (a easy-to-understand name, or short name), that is displayed in Mode Line