Document `completions-format'

* doc/emacs/mini.texi (Completion Options): Document
`completions-format'.

* lisp/simple.el (completion-list-mode): Mention in (bug#49003).

2 files changed, 11 insertions, 0 deletions

diff --git a/doc/emacs/mini.texi b/doc/emacs/mini.texi
index 2fdb1e7072f..6dcee3fa824 100644
--- a/doc/emacs/mini.texi
+++ b/doc/emacs/mini.texi
@@ -630,6 +630,14 @@ in a cyclic manner.  If you give @code{completion-cycle-threshold} a
 numeric value @var{n}, completion commands switch to this cycling
 behavior only when there are @var{n} or fewer alternatives.
 
+@vindex completions-format
+  When displaying completions, Emacs will normally pop up a new buffer
+to display the completions.  The completions will (by default) be
+sorted in columns horizontally in alphabetical order, but this can be
+changed by changing the @code{completions-format} user option.  If
+@code{vertical}, sort the completions vertically in columns instead,
+and if @code{one-column}, just use a single column.
+
 @node Minibuffer History
 @section Minibuffer History
 @cindex minibuffer history
diff --git a/lisp/simple.el b/lisp/simple.el
index 4630a11c753..fdaeb6ac22d 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -9086,6 +9086,9 @@ Type \\<completion-list-mode-map>\\[choose-completion] in the completion list\
  to select the completion near point.
 Or click to select one with the mouse.
 
+See the `completions-format' user option to control how this
+buffer is formatted.
+
 \\{completion-list-mode-map}")
 
 (defun completion-list-mode-finish ()