Modus themes 1.4.0 for GNU Emacs

Published version 1.4.0 of the Modus themes. The detailed release notes are provided below. For a general overview of the project watch the status update of 2021-05-19. For any questions pertaining to this publication feel welcome to contact me.

A patch to update the version of the themes that are shipped with Emacs will be prepared right after this announcement is published. GNU ELPA syncs from emacs.git, so expect an update shortly thereafter.


Modus themes version 1.4.0

By Protesilaos Stavrou <info@protesilaos.com> on 2021-05-25

This entry records the changes made to the project since the release of
version 1.3.0 on 2021-04-17.  There have been around 100 commits in the
meantime, as is the norm.

If you are coming from older versions, please consult the change log
entry for version 1.0.0 with regard to the breaking changes that were
introduced.

Every colour-related modification is always done in accordance with the
overarching accessibility objective of the themes for a minimum contrast
ratio of 7:1 between background and foreground values in their given
combination (the WCAG AAA standard).

URL of the official manual: <https://protesilaos.com/modus-themes>.  Or
read it with Emacs' Info reader by evaluating this form:

    (info "(modus-themes) Top")

Remember that the themes are built into Emacs version 28 (current
development target), and are available on GNU ELPA, as well as other
archives.


Customisations variables
------------------------

+ Redefined the style of 'fg-only' that 'modus-themes-diffs' accepts, so
  that it no longer uses a red-green colour coding, but applies a
  red-blue distinction instead.  The symbol 'fg-only' is a deprecated
  alias for the more descriptive 'fg-only-deuteranopia'.

  This is done because green text on a light background is one of the
  worst combinations for the purposes of legibility, as it does not
  stand out in its context and thus forces undesirable compromises.
  Whereas red and blue work well in this case, while making the style
  accessible to users with red-green colour deficiency (deuteranopia).
  To avoid inconsistencies between Modus Operandi and Modus Vivendi, we
  replace green with blue in both themes.  A full report is available in
  issue 183 which was created on April 21, 2021:
  <https://gitlab.com/protesilaos/modus-themes/-/issues/183>.

+ Introduced the boolean 'modus-themes-success-deuteranopia' which
  replaces all instances of green with blue in contexts where a
  red-green colour coding is in effect (e.g. Org TODO vs DONE keywords,
  isearch current match...).

+ Implemented 'modus-themes-mail-citations' to control the colouration
  of cited text in email-related buffers, such as Gnus or message.el.
  It accepts values nil, 'faint', and 'monochrome'.  By default (the nil
  value) the text of citations cycles through blue, green, red, yellow
  depending on the level of depth.

+ Expanded the set of options for 'modus-themes-mode-line' to encompass
  the values 'borderless-accented', 'borderless-accented-3d', and
  'borderless-accented-moody'.  Those are variations of existing styles.
  The complete list:

  - nil (default)
  - 3d
  - moody
  - borderless
  - borderless-3d
  - borderless-moody
  - accented
  - accented-3d
  - accented-moody
  - borderless-accented
  - borderless-accented-3d
  - borderless-accented-moody

+ Renamed the non-nil values that 'modus-themes-org-blocks' accepts from
  'grayscale', 'rainbow' to 'gray-background' and 'tinted-background',
  respectively.  The new symbols better describe their effect on Org
  source blocks, namely, that they affect the background of the block
  rather than the foreground.  The old symbols will still work but are
  considered deprecated aliases of the newer ones.

+ Altered the intensity of the 'modus-themes-hl-line' option
  'accented-background' to a more noticeable shade of cyan/teal.  The
  old style was too subtle to have the desired effect.  The value
  'underline-accented' is not affected by this change, as it still uses
  the same subtle background it did before in combination with a more
  pronounced underline colour.

+ Deleted all deprecation warnings that concerned the transition from
  version 0.13.0 of the themes to 1.0.0.  Those had been in effect for
  several months, spanning four tagged releases.


Faces or face groups
--------------------

+ Reconsidered the use of colour in all email-related citation faces to
  avoid exaggerations and reduce complexity.  Colour values have been
  tweaked to tone down their overall intensity, while the number of
  colours has been reduced to four.  Gnus and Mu4e have faces for more
  levels of citation depth, though those will simply repeat the
  four-colour cycle.

+ Made the 'message-mml' face look consistent with the rest of the
  buffer while composing an email by changing its foreground colour from
  a yellow to a cyan variant.

+ Refined several faces in the Notmuch group in the interest of harmony:

  - Individual message headers in 'notmuch-show-mode' use bold text in
    addition to their existing subtle background to better stand out in
    their context. The face is 'notmuch-message-summary-face'.

  - Tags are no longer set unconditionally to a bold typographic weight.
    They become such for unread threads in 'notmuch-search-mode'
    buffers, as well as for headers of 'notmuch-show-mode'.

  - Removal and addition of tags is now denoted by a strike-through and
    an underline effect, respectively, whereas before they both used
    underlines with the only difference being their colour.

  - The subject line in 'notmuch-search-mode' buffers uses the main
    foreground instead of a dimmed one.  The field of matching authors
    has a tweaked foreground to keep the tabular view easy to read.

  - All cryptography-related faces are simplified to not show a coloured
    background but only use a foreground colour instead.

+ Removed direct support for 'counsel-notmuch' as it already inherits
  from the relevant notmuch faces.  The package is thus considered
  indirectly supported.

+ Refrained from setting a background to the 'csv-separator-face' as it
  would inevitably colourise the negative space in the tabular view
  created by 'csv-align-mode'.  A red text colour is used instead, even
  though this is not common practice: it is easier to spot for small,
  single characters, such as a comma or a semicolon that is meant to
  have a special meaning.  Thanks to Kevin Fleming for reporting the
  problem and for offering feedback on the choice of colour in issue
  194: <https://gitlab.com/protesilaos/modus-themes/-/issues/194>.

+ Distinguished between ordinary links and widget buttons by removing
  the underline from the latter (the 'widget-button' face) and altering
  the shade of its foreground colour.  Such widgets are used in Emacs'
  Custom interfaces and can also be found in the default Notmuch "hello"
  buffer that runs 'notmuch-hello-mode'.

+ Tweaked the Ediff current faces to be consistent with 'diff-mode' and
  related.  In practice, this only applies when 'modus-themes-diffs' is
  set to a value of 'fg-only-deuteranopia', as it adds a dim background
  to the current diff hunk.  All other styles of 'modus-themes-diffs'
  look the same as before while using Ediff.

+ Simplified the faces of 'corfu' to match the current state of the
  upstream project.  Thanks to Daniel Mendler (its developer) for
  reporting this in issue 184:
  <https://gitlab.com/protesilaos/modus-themes/-/issues/184>.

+ Refined all Eshell faces so that the output of 'ls' is consistent with
  the overall aesthetic of the themes.  Also made 'eshell-prompt'
  inherit from 'comint-highlight-prompt' to look the same as other such
  prompts (all are configurable by 'modus-themes-prompts').

+ Revised 'eshell-prompt-extras' and 'eshell-git-prompt' to use colours
  and typographic weight that better match the style of the various
  configurations they offer.

+ Simplified 'eshell-syntax-highlighting' to inherit from the standard
  Eshell faces, where appropriate.

+ Adjusted the colour of 'centaur-tabs-active-bar-face' and removed the
  bespoke 'fg-tab-accent' colour from 'modus-themes-operandi-colors' and
  'modus-themes-vivendi-colors' that was only used by it (and which
  should have never been introduced to begin with).

+ Updated the 'tab-bar-groups' faces to match changes upstream.  Thanks
  to Fritz Grabo (its developer) for the patch in merge request 35:
  <https://gitlab.com/protesilaos/modus-themes/-/merge_requests/35>.

+ Changed the Ibuffer title and group faces to better differentiate
  between group titles and special or non-file-visiting buffers.  Thanks
  to Nicolas De Jaeghere for the patch in merge request 37:
  <https://gitlab.com/protesilaos/modus-themes/-/merge_requests/37>.

+ Ensured that all faces that denote a "success" state, or which are
  expected to be coloured in green in a red-green binary, can use an
  appropriate blue colour (or colour combination that involves blue)
  instead when 'modus-themes-success-deuteranopia' is set to a non-nil
  value.

+ Added support for the new 'bookmark-face' in Emacs version 28.  This
  means that the built-in bookmark.el library is directly supported by
  the themes.  This face can be disabled by setting 'bookmark-fontify'
  to nil.  Thanks to Mark Barton for reporting the presence of this new
  face and for providing feedback on its style in issue 189:
  <https://gitlab.com/protesilaos/modus-themes/-/issues/189>.

+ Aligned 'hes-mode' ('highlight-escape-sequences') with the standard
  font-lock faces for regexp grouping.  This means that it conforms with
  changes to the 'modus-themes-syntax' variable.

+ Reconfigured the 'org-quote' face to adapt its style depending on the
  value of 'modus-themes-org-blocks'.  The default is a subtle blue/cold
  foreground colour against the main background.  When a value of
  'gray-background' is assigned to 'modus-themes-org-blocks', the text's
  colour becomes that of the main foreground in order to maintain a good
  level of legibility.  Thanks to Rudolf Adamkovič for the feedback in
  issue 190: <https://gitlab.com/protesilaos/modus-themes/-/issues/190>.

+ Refashioned the 'show-paren-match-expression' face to make it apply a
  bespoke background colour and not override the expression's foreground
  colours.  This face is used by 'show-paren-mode' when the
  customisation variable 'show-paren-style' is set to the 'expression'
  value.  Thanks to Rudolf Adamkovič for the feedback in issue 191:
  <https://gitlab.com/protesilaos/modus-themes/-/issues/191>.

+ Made headings level 8 use a fine shade of magenta by default instead
  of gray (notwithstanding user changes to 'modus-themes-headings').
  This should have a negligible difference in Org or Outline buffers,
  but is more noticeable when editing Elisp in Emacs28 while also using
  'outline-minor-mode' and with 'outline-minor-mode-highlight' set to
  'override'.  That is because several top-level forms use that heading
  level with those configurations.


Documentation (the manual)
--------------------------

+ Incorporated a sample configuration block with all customisation
  variables and with comment annotations of their available options, in
  an attempt to make it easier for users to discover what the themes
  provide.

+ Replaced all instances of "modeline" with "mode line" for consistency
  with the Emacs style.  Thanks to Rudolf Adamkovič for the patch that
  started this process in merge request 33:
  <https://gitlab.com/protesilaos/modus-themes/-/merge_requests/33>.

+ Wrote note on setting mode line faces that indicate the state of
  'god-mode'.  Thanks to Rudolf Adamkovič for the feedback in issue 187:
  <https://gitlab.com/protesilaos/modus-themes/-/issues/187>.  Also
  thanks to Rudolf for updating the applicable hook in merge request 34:
  <https://gitlab.com/protesilaos/modus-themes/-/merge_requests/34>.

+ Listed 'org-mode' variables that affect fontification in blocks:
  'org-src-fontify-natively', 'org-fontify-whole-block-delimiter-line',
  and 'org-fontify-quote-and-verse-blocks'.  This complements the
  already documented variables 'org-fontify-whole-heading-line' and
  'org-fontify-done-headline' that pertain to headings.

+ Included note on fontifying inline Latex expressions in Org buffers.
  Thanks to Rudolf Adamkovič for the feedback in issue 190:
  <https://gitlab.com/protesilaos/modus-themes/-/issues/190>.

+ Elaborated on the use of 'face-remap-add-relative' by means of sample
  code that cycles through arbitrary colours for the 'region' face.
  This is filed under the "Do It Yourself" (DIY) section.

+ Provided a DIY method for adapting the fontification of Org source
  block delimiter lines to the value of 'modus-themes-org-blocks'.

+ Expanded the DIY entry on overriding the saturation of the active
  theme's colours with a method that combines the programmatic approach
  with manual overrides.  The user can thus specify the colour values
  they want to override and let the rest be handled by Elisp.

+ Introduced a section with answers to Frequently Asked Questions (FAQ)
  about the design of the themes as well as recommendations on how to
  ensure optimal reading conditions or start thinking about them.  The
  questions are:

  - Is the contrast ratio about adjacent colors?
  - What does it mean to avoid exaggerations?
  - Why are colors mostly variants of blue, magenta, cyan?
  - What is the best setup for legibility?


Miscellaneous
-------------

+ Removed superfluous code from internal functions and adapted their
  indentation to make them easier to read.

+ Recalibrated some values in 'modus-themes-vivendi-colors' to ensure
  consistency in luminance with other colours that are used in their
  context.  Those are subtle changes that can only be discerned in
  side-by-side comparisons of the before and after states.  Thanks to
  André Alexandre Gomes for the feedback in issue 193:
  <https://gitlab.com/protesilaos/modus-themes/-/issues/193>.

+ Changed the saturation and hueness of the bespoke 'fg-comment-yellow'
  in 'modus-themes-operandi-colors' and 'modus-themes-vivendi-colors' to
  better contrast with its context, while still keeping its luminance
  consistent with its role as a colour for comments in code.  This is
  used when 'modus-themes-syntax' is configured appropriately (read its
  doc string or consult the manual).

+ Attempted to add explicit support for the faces of the built-in
  pulse.el library, but ultimately opted against them as the doc string
  of 'pulse-highlight-face' advises against customising it, even though
  it is not clear from the source code in emacs.git what the problem
  could be.  We shall reconsider this case for the next release cycle.
  Thanks to Gustavo Barros for the feedback on several aspects of this
  topic in issues 185 and 200:

  - <https://gitlab.com/protesilaos/modus-themes/-/issues/185>
  - <https://gitlab.com/protesilaos/modus-themes/-/issues/200>

+ Took the feedback of John Haman in issue 199 as a reminder to complete
  the set of possible values for the 'modus-themes-mode-line' variable:
  <https://gitlab.com/protesilaos/modus-themes/-/issues/199>.