Improve filling-related documentation

* doc/emacs/text.texi (Auto Fill, Fill Commands): Mention special
line-breaking rules for CJK characters and the kinsoku rules.
(Bug#47856)

* lisp/textmodes/fill.el
(fill-separate-heterogeneous-words-with-space): Doc fix.

1 files changed, 6 insertions, 4 deletions

diff --git a/lisp/textmodes/fill.el b/lisp/textmodes/fill.el
index e9bef6ec801..6d283bd6f14 100644
--- a/lisp/textmodes/fill.el
+++ b/lisp/textmodes/fill.el
@@ -51,10 +51,12 @@ A value of nil means that any change in indentation starts a new paragraph."
 
 (defcustom fill-separate-heterogeneous-words-with-space nil
   "Non-nil means to use a space to separate words of a different kind.
-This will be done with a word in the end of a line and a word in
-the beginning of the next line when concatenating them for
-filling those lines.  Whether to use a space depends on how the
-words are categorized."
+For example, when an English word at the end of a line and a CJK word
+at the beginning of the next line are joined into a single line, they
+will be separated by a space if this variable is non-nil.
+Whether to use a space to separate such words also depends on the entry
+in `fill-nospace-between-words-table' for the characters before and
+after the newline."
   :type 'boolean
   :group 'fill
   :version "26.1")