Document the shorthand hints displayed by M-x

* doc/emacs/m-x.texi (M-x): Document the numeric meaning of
suggest-key-bindings.  Document the shorthand hints for commands
that have no key bindings.  Document that M-x completion ignores
obsolete commands.

* etc/NEWS: Move the M-x entry to "Editing Changes" and mark it as
documented.

2 files changed, 20 insertions, 2 deletions

diff --git a/doc/emacs/m-x.texi b/doc/emacs/m-x.texi
index c9ae559f984..795d6fe373b 100644
--- a/doc/emacs/m-x.texi
+++ b/doc/emacs/m-x.texi
@@ -43,6 +43,13 @@ Note that @code{forward-char} is the same command that you invoke with
 the key @kbd{C-f}.  The existence of a key binding does not stop you
 from running the command by name.
 
+@cindex obsolete command
+  When @kbd{M-x} completes on commands, it ignores the commands that
+are declared @dfn{obsolete}; for these, you will have to type their
+full name.  Obsolete commands are those for which newer, better
+alternatives exist, and which are slated for removal in some future
+Emacs release.
+
   To cancel the @kbd{M-x} and not run a command, type @kbd{C-g} instead
 of entering the command name.  This takes you back to command level.
 
@@ -57,7 +64,16 @@ mentions this in the echo area after running the command.  For
 example, if you type @kbd{M-x forward-word}, the message says that you
 can run the same command by typing @kbd{M-f}.  You can turn off these
 messages by setting the variable @code{suggest-key-bindings} to
-@code{nil}.
+@code{nil}.  The value of @code{suggest-key-bindings} can also be a
+number, in which case Emacs will show the binding for that many
+seconds before removing it from display.  The default behavior is to
+display the binding for 2 seconds.
+
+  Commands that don't have key bindings, can still be invoked after
+typing less than their full name at the @samp{M-x} prompt.  Emacs
+mentions such shorthands in the echo area if they are significantly
+shorter than the full command name.  The setting of
+@code{suggest-key-bindings} affects these hints as well.
 
   In this manual, when we speak of running a command by name, we often
 omit the @key{RET} that terminates the name.  Thus we might say
diff --git a/etc/NEWS b/etc/NEWS
index bd8edee5538..8a3bd8e30bd 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -148,7 +148,6 @@ the `network-security-level' variable.
 +++
 ** C-h l now also lists the commands that were run.
 
-** M-x suggests shorthands and ignores obsolete commands for completion.
 ** x-select-enable-clipboard is renamed select-enable-clipboard.
 x-select-enable-primary and renamed select-enable-primary.
 Additionally they both now apply to all systems (OSX, GNUstep, Windows, you
@@ -316,6 +315,9 @@ at configure time.
 
 * Editing Changes in Emacs 25.1
 
++++
+** M-x suggests shorthands and ignores obsolete commands for completion.
+
 ** Successive single-char deletions are collapsed in the undo-log just like
 successive char insertions.