Improve `sentence-end-double-space` docstring

* lisp/textmodes/paragraphs.el (sentence-end-double-space):
Improve and expand docstring.

(cherry picked from commit b2d99c0d0aaab4d0c7026a26393e22d66246a349)

diff --git a/lisp/textmodes/paragraphs.el b/lisp/textmodes/paragraphs.el
index af99a96e045bbc6d5c12285fb1f4f5aaa9afd805..be741e6517b743f58eda56fede6f43296b7a5cec 100644 (file)
--- a/lisp/textmodes/paragraphs.el
+++ b/lisp/textmodes/paragraphs.el
@@ -118,8 +118,28 @@ text indented by a margin setting."
 
 (defcustom sentence-end-double-space t
   "Non-nil means a single space does not end a sentence.
-This is relevant for filling.  See also `sentence-end-without-period'
-and `colon-double-space'.
+This user option affects fill commands and sentence commands.
+
+If this variable is non-nil, Emacs considers a period followed by two
+spaces or by a newline as the end of a sentence.  This means that:
+
+    1. The fill commands will not break a line after a period followed
+       by just one space.
+
+    2. The sentence commands stop only for double spaces.
+
+If this variable is nil, Emacs considers a period followed by one space
+or by a newline as the end of a sentence.  This means that:
+
+    1. The fill commands will break a line after a period followed by
+       one space, and put just one space after each period.
+
+    2. The sentence commands stop for single spaces.
+
+For more details, see Info node `(emacs) Fill Commands' and Info
+node `(emacs) Sentences'.
+
+See also `sentence-end-without-period' and `colon-double-space'.
 
 This value is used by the function `sentence-end' to construct the
 regexp describing the end of a sentence, when the value of the variable