Typically, grave accents and apostrophes are treated specially in
documentation strings and diagnostic messages, and translate to matching
single quotation marks (also called “curved quotes”). For example,
the documentation string "Alias for `foo'." and the function call
(message "Alias for `foo'.") both translate to "Alias for
‘foo’.". Less commonly, Emacs displays grave accents and apostrophes
as themselves, or as apostrophes only (e.g., "Alias for 'foo'.").
Documentation strings and message formats should be written so that
they display well with any of these styles. For example, the
documentation string "Alias for 'foo'." is probably not what you
want, as it can display as "Alias for ’foo’.", an unusual style in
English.
Sometimes you may need to display a grave accent or apostrophe
without translation, regardless of text quoting style. In a
documentation string, you can do this with escapes. For example, in
the documentation string "\\=`(a ,(sin 0)) ==> (a 0.0)" the grave
accent is intended to denote Lisp code, so it is escaped and displays
as itself regardless of quoting style. In a call to message or
error, you can avoid translation by using a format "%s"
with an argument that is a call to format. For example,
(message "%s" (format "`(a ,(sin %S)) ==> (a %S)" x (sin x)))
displays a message that starts with grave accent regardless of text
quoting style.
The value of this user option is a symbol that specifies the style
Emacs should use for single quotes in the wording of help and
messages. If the option’s value is curve, the style is
‘like this’ with curved single quotes. If the value is
straight, the style is 'like this' with straight
apostrophes. If the value is grave, quotes are not translated
and the style is `like this' with grave accent and apostrophe, the
standard style before Emacs version 25. The default value nil
acts like curve if curved single quotes seem to be displayable,
and like grave otherwise.
This option is useful on platforms that have problems with curved quotes. You can customize it freely according to your personal preference.
You should not read the value of the variable
text-quoting-style directly. Instead, use this function with
the same name to dynamically compute the correct quoting style on the
current terminal in the nil case described above.