Improve documentation of 'copy-sequence'

* src/fns.c (Fcopy_sequence):
* doc/lispref/sequences.texi (Sequence Functions): Mention the
exception when copying an empty sequence.  (Bug#28627)

1 files changed, 3 insertions, 1 deletions

diff --git a/src/fns.c b/src/fns.c
index 4524ff9b268..2311a6e041b 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -482,7 +482,9 @@ usage: (vconcat &rest SEQUENCES)   */)
 DEFUN ("copy-sequence", Fcopy_sequence, Scopy_sequence, 1, 1, 0,
        doc: /* Return a copy of a list, vector, string, char-table or record.
 The elements of a list, vector or record are not copied; they are
-shared with the original.  */)
+shared with the original.
+If the original sequence is empty, this function may return
+the same empty object instead of its copy.  */)
   (Lisp_Object arg)
 {
   if (NILP (arg)) return arg;