logos.el: simple focus mode for Emacs with page breaks or outlines

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logos.el: simple focus mode for Emacs with page breaks or outlines

Copyright (C) 2022-2023 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.”

(a) The FSF’s Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”

This manual, written by Protesilaos Stavrou, describes the customization options for ‘logos’ (or ‘logos.el’), and provides every other piece of information pertinent to it.

The documentation furnished herein corresponds to stable version 1.1.0, released on 2023-06-20. Any reference to a newer feature which does not yet form part of the latest tagged commit, is explicitly marked as such.

Current development target is 1.2.0-dev.

1 Overview

This package provides a simple “focus mode” which can be applied to any buffer for reading, writing, or even doing a presentation. The buffer can be divided in pages using the page-delimiter, outline structure, or any other pattern. Commands are provided to move between those pages. These motions work even when narrowing is in effect (and they preserve it). ‘logos.el’ is designed to be simple by default and easy to extend. This manual provides concrete examples to that end.

What constitutes a page delimiter is determined by the user options logos-outlines-are-pages and logos-outline-regexp-alist. By default, this only corresponds to the ‘^L’ character (which can be inserted using the standard keys with ‘C-q C-l’).

Logos does not define any key bindings. Try something like this, if you want:

(let ((map global-map))
  (define-key map [remap narrow-to-region] #'logos-narrow-dwim)
  (define-key map [remap forward-page] #'logos-forward-page-dwim)
  (define-key map [remap backward-page] #'logos-backward-page-dwim))

On standard Emacs, those key bindings are: ‘C-x n n’, ‘C-x ]’, ‘C-x [’. The logos-narrow-dwim is not necessary for users who already know how to narrow effectively. Such users may still want to bind it to a key.

For users running Emacs version 28 or higher, Logos defines the logos-repeat-map which is activated when repeat-mode is enabled. This means that page motions, ‘C-x ]’ and ‘C-x [’, can be repeated by following them up with either ‘]’ or ‘[’. The repetition stops when another command is invoked.

Logos provides some optional aesthetic tweaks which come into effect when the buffer-local logos-focus-mode is enabled. These will hide the cursor (logos-hide-cursor), hide the mode line (logos-hide-mode-line), disable the buffer boundary indicators (indicate-buffer-boundaries), enable scroll-lock-mode (logos-scroll-lock), use variable-pitch-mode in non-programming buffers (logos-variable-pitch), make the buffer read-only (logos-buffer-read-only), center the buffer in its window if the ‘olivetti’ package is installed (logos-olivetti), and hide the fringe face (logos-hide-fringe). All these variables are buffer-local.

Furthermore, the logos-focus-mode establishes a bespoke keymap, which can be used to, for example, bind the arrow keys to page motions. The keymap is logos-focus-mode-map and is empty by default (we do not define any keys and trust the user to pick their own).

Logos is the familiar word derived from Greek (watch my presentation on philosophy about Cosmos, Logos, and the living universe: https://protesilaos.com/books/2022-02-05-cosmos-logos-living-universe/), though it also stands for these two perhaps equally insightful backronyms about the mechanics of this package:

  1. ^L’ Only Generates Ostensible Slides
  2. Logos Optionally Goes through Outline Sections

2 Installation

2.1 GNU ELPA package

The package is available as ‘logos’. Simply do:

M-x package-refresh-contents
M-x package-install

And search for it.

GNU ELPA provides the latest stable release. Those who prefer to follow the development process in order to report bugs or suggest changes, can use the version of the package from the GNU-devel ELPA archive. Read: https://protesilaos.com/codelog/2022-05-13-emacs-elpa-devel/.

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2.2 Manual installation

Assuming your Emacs files are found in ‘~/.emacs.d/’, execute the following commands in a shell prompt:

cd ~/.emacs.d

# Create a directory for manually-installed packages
mkdir manual-packages

# Go to the new directory
cd manual-packages

# Clone this repo, naming it "logos"
git clone https://git.sr.ht/~protesilaos/logos logos

Finally, in your ‘init.el’ (or equivalent) evaluate this:

;; Make Elisp files in that directory available to the user.
(add-to-list 'load-path "~/.emacs.d/manual-packages/logos")

Everything is in place to set up the package.

3 Sample configuration

Logos does not bind its own keys and does not make any opinionated changes out-of-the-box (Extra tweaks):

(require 'logos)

;; If you want to use outlines instead of page breaks (the ^L):
(setq logos-outlines-are-pages t)

;; This is the default value for the outlines:
(setq logos-outline-regexp-alist
      `((emacs-lisp-mode . "^;;;+ ")
        (org-mode . "^\\*+ +")
        (markdown-mode . "^\\#+ +")))

;; These apply when `logos-focus-mode' is enabled.  Their value is
;; buffer-local.
(setq-default logos-hide-cursor nil
              logos-hide-mode-line t
              logos-hide-buffer-boundaries t
              logos-hide-fringe t
              logos-variable-pitch nil
              logos-buffer-read-only nil
              logos-scroll-lock nil
              logos-olivetti nil)

;; Also check this manual for `logos-focus-mode-hook'.  It lets you
;; extend `logos-focus-mode'.

(let ((map global-map))
  (define-key map [remap narrow-to-region] #'logos-narrow-dwim)
  (define-key map [remap forward-page] #'logos-forward-page-dwim)
  (define-key map [remap backward-page] #'logos-backward-page-dwim)
  (define-key map (kbd "<f9>") #'logos-focus-mode))

;; Also consider adding keys to `logos-focus-mode-map'.  They will take
;; effect when `logos-focus-mode' is enabled.

4 Extra tweaks

This section contains snippets of code that extend the functionality of ‘logos’. These either apply to logos-focus-mode or enhance the page motions through the logos-page-motion-hook.

4.1 Center the buffer in its window

Install the excellent ‘olivetti’ package by Paul W. Rankin. Then set logos-olivetti to non-nil.

The present author’s favourite settings given a fill-column of ‘72’:

(setq olivetti-body-width 0.7
      olivetti-minimum-body-width 80
      olivetti-recall-visual-line-mode-entry-state t)

Though note that Olivetti works well even without a fill-column and auto-fill-mode disabled.

4.2 Make EWW look like the rest of Emacs

By default, all ‘M-x eww’ buffers use the shr-max-width which is set to 120 characters. This is above the standard value of fill-column and thus does not let text flow nicely while using ‘olivetti’ package (Center the buffer in its window).

For a general customization, the user can evaluate this:

(setq shr-max-width fill-column)

EWW buffers also default to variable-pitch typography by default (as opposed to whatever the font family of the default face is). This too can be made consistent with the rest of Emacs:

(setq shr-use-fonts nil)

[ For font-related customizations check the ‘fontaine’ package on GNU ELPA (by Protesilaos). ]

Note that all variables with the ‘shr-’ prefix are about the built-in Simple HTML Renderer, so they will affect any other package that relies on them beside EWW (in principle, the aforementioned should not pose any problem).

4.3 Automatically reveal Org or Outline subtree

The Logos page motions normally jump between positions. Though Org and Outline require that Logos also reveals the headings’ contents. This is necessary to avoid invisible motions inside a folded heading that contains subheadings. The unfolding only applies to the current entry. This is the relevant snippet from ‘logos.el’:

(defun logos-reveal-entry ()
  "Reveal Org or Outline entry."
   ((and (eq major-mode 'org-mode)
   ((or (eq major-mode 'outline-mode)
        (bound-and-true-p outline-minor-mode))

(add-hook 'logos-page-motion-hook #'logos-reveal-entry)

Users may prefer to reveal the entire subtree instead of the current entry: the heading at point and all of its subheadings. In this case, one may override the definition of logos-reveal-entry:

;; glue code to expand an Org/Outline heading
(defun logos-reveal-entry ()
  "Reveal Org or Outline entry."
   ((and (eq major-mode 'org-mode)
   ((or (eq major-mode 'outline-mode)
        (bound-and-true-p outline-minor-mode))

4.4 Recenter at the top upon page motion

Page motions normally reposition the point at the centre of the window if necessary (this is standard Emacs behaviour). To always change the placement invoke the recenter function with a numeric argument.

;; place point at the top when changing pages
(defun my-logos-recenter-top ()
  "Use `recenter' to reposition the view at the top."
  (recenter 0))

(add-hook 'logos-page-motion-hook #'my-logos-recenter-top)

The ‘0’ argument refers to the topmost line. So ‘1’ points to the line below and so on.

If the recentering should not affect specific modes, tweak the function accordingly:

(defvar my-logos-no-recenter-top-modes 
  '(emacs-lisp-mode lisp-interaction-mode))

(defun my-logos-recenter-top ()
  "Use `recenter' to reposition the view at the top."
  (unless (memq major-mode my-logos-no-recenter-top-modes)
    (recenter 0)))

Or simply exclude all programming modes:

(defun my-logos-recenter-top ()
  "Use `recenter' to reposition the view at the top."
  (unless (derived-mode-p 'prog-mode)
    (recenter 0)))

4.5 Use outlines and page breaks

By default, the page motions only move between the ‘^L’ delimiters. While the option logos-outlines-are-pages changes the behaviour to move between outline headings instead. What constitutes an “outline heading” is determined by the logos-outline-regexp-alist with an automatic fallback to either outline-regexp or page-delimiter (Logos handles this fallback condition internally).

Provided this:

(setq logos-outlines-are-pages t)

The default value of logos-outline-regexp-alist will affect org-mode, emacs-lisp-mode, and any of their derivatives (e.g. lisp-interaction-mode (the standard scratch buffer) is based on emacs-lisp-mode). Its fallback value is whatever the major mode sets as an outline, else the standard ‘^L’.

(setq logos-outline-regexp-alist
      `((emacs-lisp-mode . "^;;;+ ")
        (org-mode . "^\\*+ +")))

It is possible to tweak those regular expressions to target both the outline and the page delimiters:

(setq logos-outline-regexp-alist
      `((emacs-lisp-mode . ,(format "\\(^;;;+ \\|%s\\)" logos-page-delimiter))
        (org-mode . ,(format "\\(^\\*+ +\\|%s\\)" logos-page-delimiter))))

The form ‘,(format "\\(^;;;+ \\|%s\\)" logos-page-delimiter)’ expands to ‘"\\(^;;;+ \\|^^L\\)"’ where ‘^L’ is the actual control character.

For Org it may be better to either not target the ‘^L’ or to also target the horizontal rule (five hyphens on a line, else the ‘^-\\{5\\}$’ pattern). Putting it all together:

(setq logos-outline-regexp-alist
      `((emacs-lisp-mode . ,(format "\\(^;;;+ \\|%s\\)" logos-page-delimiter))
        (org-mode . ,(format "\\(^\\*+ +\\|^-\\{5\\}$\\|%s\\)" logos-page-delimiter))))

Another Org-specific tweak is to use heading levels up to a specific number. The idea would be that anything below that number is not significant. For example, ‘^\\* +’ only applies to top-level headings, while ‘^\\*\\{1,3\\} +’ covers heading levels 1 through 3. Accounting for the aforementiond horizontal rule and generic page delimiter, the end result can look like this:

(setq logos-outline-regexp-alist
      `((emacs-lisp-mode . ,(format "\\(^;;;+ \\|%s\\)" logos-page-delimiter))
        (org-mode . ,(format "\\(^\\*\\{1,3\\} +\\|^-\\{5\\}$\\|%s\\)" logos-page-delimiter))))

4.6 Leverage logos-focus-mode-hook

The logos-focus-mode-hook is a normal hook that runs when logos-focus-mode is enabled. Each function is called without an argument and looks like those in ‘logos.el’. An example that sets a variable is logos--buffer-read-only; one that sets a mode is logos--scroll-lock; another that sets the mode of an external package is logos--olivetti; while logos--hide-fringe provides yet another useful sample.

If a function cannot be like the aforementioned though still needs to set its state both when logos-focus-mode is enabled and disabled, then use the logos-focus-mode-hook instead.

4.6.1 Conditionally toggle org-indent-mode

Here is a snippet that relies on the logos-focus-mode-hook to extend the functionality of logos-focus-mode (Leverage logos-focus-mode-hook).

(defvar my-logos-org-indent nil
  "When t, disable `org-indent-mode' during `logos-focus-mode'.")

(defun my-logos-org-indent ()
  "Set `my-logos-org-indent' in `logos-focus-mode'."
  (when my-logos-org-indent
    ;; Disable `org-indent-mode' when `logos-focus-mode' is enabled and
    ;; restore it when `logos-focus-mode' is disabled.  The
    ;; `logos-set-mode-arg' function takes care of the technicalities.
    (logos-set-mode-arg 'org-indent-mode -1)))

(add-hook 'logos-focus-mode-hook #'my-logos-org-indent)

The my-logos-org-indent variable lets the user opt in and out of this feature, by setting it to t or nil, respectively. If such a toggle is not needed, the following will suffice:

(defun my-logos-org-indent ()
  "Set `my-logos-org-indent' in `logos-focus-mode'."
  ;; Disable `org-indent-mode' when `logos-focus-mode' is enabled and
  ;; restore it when `logos-focus-mode' is disabled.  The
  ;; `logos-set-mode-arg' function takes care of the technicalities.
  (logos-set-mode-arg 'org-indent-mode -1))

(add-hook 'logos-focus-mode-hook #'my-logos-org-indent)

4.6.2 Disable menu-bar and tool-bar

Continuing with the examples in this section of the manual, this is how to disable the menu-bar-mode and tool-bar-mode when activating the logos-focus-mode.

;; Assuming the `menu-bar-mode' is enabled by default...
(defun my-logos-hide-menu-bar ()
  (logos-set-mode-arg 'menu-bar-mode -1))

(add-hook 'logos-focus-mode-hook #'my-logos-hide-menu-bar)

;; Assuming the `tool-bar-mode' is enabled by default...
(defun my-logos-hide-tool-bar ()
  (logos-set-mode-arg 'tool-bar-mode -1))

(add-hook 'logos-focus-mode-hook #'my-logos-hide-tool-bar)

If those modes are already disabled, the following have no effect. Otherwise they toggle the bars off while logos-focus-mode is enabled and then restore them back on when logos-focus-mode is disabled.

4.7 Update fringe color on theme switch

The user option logos-hide-fringe does not actually remove the fringe, as that would change the user’s preference for fringe-mode. Instead, it remaps its background color to be the same as that of the default face. For example, if the main background is white while the fringe is gray, the fringe will become white as well.

The problem with this approach is that the color is not automatically updated upon switching to a new theme, such as by toggling between one with a light background to another with a dark one. The solution is to assign the logos-update-fringe-in-buffers function to a hook that is triggered by the theme-loading operation.

Some themes provide such a hook. For example, the ‘modus-themes’ package has the modus-themes-after-load-theme-hook (the themes ‘modus-operandi’ and ‘modus-vivendi’ are built into Emacs version 28 or higher).

(add-hook 'modus-themes-after-load-theme-hook #'logos-update-fringe-in-buffers)

A user-defined, theme-agnostic setup for such a hook can be configured thus:

(defvar after-enable-theme-hook nil
  "Normal hook run after enabling a theme.")

(defun run-after-enable-theme-hook (&rest _args)
  "Run `after-enable-theme-hook'."
  (run-hooks 'after-enable-theme-hook))

(advice-add 'enable-theme :after #'run-after-enable-theme-hook)

Then use it like this:

(add-hook 'after-enable-theme-hook #'logos-update-fringe-in-buffers)

5 Acknowledgements

Logos is meant to be a collective effort. Every bit of help matters.


Protesilaos Stavrou.

Contributions to code or the manual

Daniel Mendler, Edgar Vincent, Lucy McPhail, Omar Antolín Camarena, Philip Kaludercic, Remco van ’t Veer, and user Ypot.

Ideas and/or user feedback

Daniel Mendler, Dave Abrahams, Marcel Ventosa, Xiaoduan, Ypot.

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    In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”


    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.


    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.


    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.


    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.


    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/licenses/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.


    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

  Copyright (C)  year  your name.
  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.3
  or any later version published by the Free Software Foundation;
  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
  Texts.  A copy of the license is included in the section entitled ``GNU
  Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with…Texts.” line with this:

    with the Invariant Sections being list their titles, with
    the Front-Cover Texts being list, and with the Back-Cover Texts
    being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

B Indices