emacs-28 817c929: Doc fix for concat

[Stefan Kangas]

branch: emacs-28
commit 817c929edaf77dbdcd2ce7b9e6bbd3a5c57604f1
Author: Ihor Radchenko <yantar92@gmail.com>
Commit: Stefan Kangas <stefan@marxist.se>

    Doc fix for concat
    
    * src/fns.c (Fconcat): Note that composition values may not remain eq
    in return value of concat.  (Bug#48740)
---
 src/fns.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/fns.c b/src/fns.c
index a72e41a..6f358dd 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -672,6 +672,9 @@ DEFUN ("concat", Fconcat, Sconcat, 0, MANY, 0,
        doc: /* Concatenate all the arguments and make the result a string.
 The result is a string whose elements are the elements of all the arguments.
 Each argument may be a string or a list or vector of characters (integers).
+
+Values of the `composition' property of the result are not guaranteed
+to be `eq'.
 usage: (concat &rest SEQUENCES)  */)
   (ptrdiff_t nargs, Lisp_Object *args)
 {