master 3848e27: Improve the documentation of a recent change

[Eli Zaretskii]

branch: master
commit 3848e2727edab4a2bcb6bca52abae883e33ac90b
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Improve the documentation of a recent change
    
    * etc/NEWS:
    * doc/lispref/sequences.texi (Sequence Functions): Improve
    documentation of 'seq-union'.
---
 doc/lispref/sequences.texi | 8 +++++---
 etc/NEWS                   | 3 ++-
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index 53d3719..4a48d62 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -957,9 +957,11 @@ contain less elements than @var{n}.  @var{n} must be an 
integer.  If
 @cindex sequences, union of
 @cindex union of sequences
   This function returns a list of the elements that appear either in
-@var{sequence1} or @var{sequence2}.  If the optional argument
-@var{function} is non-@code{nil}, it is a function of two arguments to
-use to compare elements instead of the default @code{equal}.
+@var{sequence1} or @var{sequence2}.  The elements of the returned list
+are all unique, in the sense that no two elements there will compare
+equal.  If the optional argument @var{function} is non-@code{nil}, it
+should be a function of two arguments to use to compare elements,
+instead of the default @code{equal}.
 
 @example
 @group
diff --git a/etc/NEWS b/etc/NEWS
index b1ad4dd..b10aa3b 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -3858,7 +3858,8 @@ supporting Lisp files when 'require' is unsuitable.
 +++
 ** New function 'seq-union'.
 This function takes two sequences and returns a list of all elements
-that appear in either of them.
+that appear in either of them, with no two elements that compare equal
+appearing in the result.
 
 +++
 ** New function 'syntax-class-to-char'.