diff --git a/doc/lispref/commands.texi b/doc/lispref/commands.texi
index 0a324a642fe..9a396f57ef0 100644
--- a/doc/lispref/commands.texi
+++ b/doc/lispref/commands.texi
@@ -3000,7 +3000,7 @@ causes it to evaluate @code{help-form} and display the result.  It
 then continues to wait for a valid input character, or keyboard-quit.
 @end defun
 
-@defun read-multiple-choice prompt choices
+@defun read-multiple-choice prompt choices &optional help-string
 Ask user a multiple choice question.  @var{prompt} should be a string
 that will be displayed as the prompt.
 
@@ -3010,6 +3010,11 @@ entry to be displayed while prompting (if there's room, it might be
 shortened), and the third, optional entry is a longer explanation that
 will be displayed in a help buffer if the user requests more help.
 
+If optional argument @var{help-string} is non-@code{nil}, it should be
+a string with a more detailed description of all choices.  It will be
+displayed in a help buffer instead of the default auto-generated
+description when the user types @kbd{?}.
+
 The return value is the matching value from @var{choices}.
 
 @lisp
diff --git a/src/editfns.c b/src/editfns.c
index 5c9c34dc352..6ba09cceec4 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -1233,7 +1233,11 @@ return "unknown".
 If optional argument UID is an integer, return the full name
 of the user with that uid, or nil if there is no such user.
 If UID is a string, return the full name of the user with that login
-name, or nil if there is no such user.  */)
+name, or nil if there is no such user.
+
+If the full name includes commas, remove everything starting with
+the first comma, because the \\='gecos\\=' field of the \\='/etc/passwd\\=' file
+is in general a comma-separated list.  */)
   (Lisp_Object uid)
 {
   struct passwd *pw;
@@ -1263,7 +1267,8 @@ name, or nil if there is no such user.  */)
     return Qnil;
 
   p = USER_FULL_NAME;
-  /* Chop off everything after the first comma. */
+  /* Chop off everything after the first comma, since 'pw_gecos' is a
+     comma-separated list. */
   q = strchr (p, ',');
   full = make_string (p, q ? q - p : strlen (p));