Some doc for delete-duplicate-lines

* doc/emacs/killing.texi (Deletion): Mention delete-duplicate-lines.

* lisp/sort.el (delete-duplicate-lines): Doc fix.

* etc/NEWS: Related edit.

2 files changed, 15 insertions, 0 deletions

diff --git a/doc/emacs/ChangeLog b/doc/emacs/ChangeLog
index 7e42d0fcaba..ac8c13ddf1d 100644
--- a/doc/emacs/ChangeLog
+++ b/doc/emacs/ChangeLog
@@ -1,3 +1,7 @@
+2014-01-26  Glenn Morris  <rgm@gnu.org>
+
+        * killing.texi (Deletion): Mention delete-duplicate-lines.
+
 2014-01-24  Glenn Morris  <rgm@gnu.org>
 
         * ack.texi (Acknowledgments): No longer mention obsolete xesam.el,
diff --git a/doc/emacs/killing.texi b/doc/emacs/killing.texi
index 52adbb85431..1da226971eb 100644
--- a/doc/emacs/killing.texi
+++ b/doc/emacs/killing.texi
@@ -136,6 +136,17 @@ the current line).  On a solitary blank line, it deletes that line.
 previous line, by deleting a newline and all surrounding spaces, usually
 leaving a single space.  @xref{Indentation,M-^}.
 
+@c Not really sure where to put this...
+@findex delete-duplicate-lines
+  The command @code{delete-duplicate-lines} searches the region for
+identical lines, and removes all but one copy of each.  Normally it
+keeps the first instance of each repeated line, but with a @kbd{C-u}
+prefix argument it keeps the last.  With a @kbd{C-u C-u} prefix
+argument, it only searches for adjacent identical lines.  This is a
+more efficient mode of operation, useful when the lines have already
+been sorted.  With a @kbd{C-u C-u C-u} prefix argument, it retains
+repeated blank lines.
+
 @node Killing by Lines
 @subsection Killing by Lines