Document return values of the various read-* functions

* lisp/textmodes/string-edit.el (read-string-from-buffer):
* lisp/simple.el (read-from-kill-ring, read-shell-command)
(read-signal-name):
* lisp/replace.el (read-regexp-case-fold-search):
* lisp/auth-source.el (read-passwd):
* lisp/subr.el (read-key, read-number):
* lisp/minibuffer.el (read-file-name, read-no-blanks-input):
* lisp/international/mule-cmds.el (read-multilingual-string):
* lisp/language/japan-util.el (read-hiragana-string):
* lisp/files-x.el (read-file-local-variable)
(read-file-local-variable-mode, read-file-local-variable-value):
* lisp/faces.el (read-face-font, read-face-name):
* lisp/simple.el (read-extended-command):
* lisp/env.el (read-envvar-name):
* lisp/files.el (read-directory-name):
* lisp/faces.el (read-color):
* lisp/international/mule-diag.el (read-charset):
* lisp/emacs-lisp/map-ynp.el (read-answer):
* src/coding.c (Fread_coding_system)
(Fread_non_nil_coding_system):
* src/minibuf.c (Fread_command, Fread_from_minibuffer):
* src/lread.c (Fread_char, Fread_char_exclusive, Fread_event): Doc
fixes.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/coding.c b/src/coding.c
index b8ed3a35957..619a362d328 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -8625,7 +8625,8 @@ about coding-system objects.  */)
 
 DEFUN ("read-non-nil-coding-system", Fread_non_nil_coding_system,
        Sread_non_nil_coding_system, 1, 1, 0,
-       doc: /* Read a coding system from the minibuffer, prompting with string PROMPT.  */)
+       doc: /* Read a coding system from the minibuffer, prompting with string PROMPT.
+Return the symbol of the coding-system.  */)
   (Lisp_Object prompt)
 {
   Lisp_Object val;
@@ -8641,6 +8642,8 @@ DEFUN ("read-non-nil-coding-system", Fread_non_nil_coding_system,
 DEFUN ("read-coding-system", Fread_coding_system, Sread_coding_system, 1, 2, 0,
        doc: /* Read a coding system from the minibuffer, prompting with string PROMPT.
 If the user enters null input, return second argument DEFAULT-CODING-SYSTEM.
+Return the coding-system's symbol, or nil if both the user input and
+DEFAULT-CODING-SYSTEM are empty or null.
 Ignores case when completing coding systems (all Emacs coding systems
 are lower-case).  */)
   (Lisp_Object prompt, Lisp_Object default_coding_system)