diff --git a/doc/emacs/files.texi b/doc/emacs/files.texi
index 7f514a1c8b7..ccdeef414e2 100644
--- a/doc/emacs/files.texi
+++ b/doc/emacs/files.texi
@@ -779,6 +779,12 @@ operations typically break hard links, disconnecting the file name you
 visited from any alternate names for the same file.  This has nothing
 to do with Emacs---the version control system does it.
 
+  Some file storage services support @dfn{file versioning}: they
+record history of previous versions of files, and allow reverting to
+those previous versions.  If you want to be able to do that with files
+hosted by those services when editing them with Emacs, customize
+@code{backup-by-copying} to a non-@code{nil} value.
+
 @node Customize Save
 @subsection Customizing Saving of Files
 
diff --git a/lisp/keymap.el b/lisp/keymap.el
index d2544e30ce0..b2b475c7d71 100644
--- a/lisp/keymap.el
+++ b/lisp/keymap.el
@@ -260,7 +260,7 @@ returned by \\[describe-key] (`describe-key')."
                         (setq word (concat (match-string 1 word)
                                            (match-string 3 word)))
                         (not (string-match
-                              "\\<\\(NUL\\|RET\\|LFD\\|ESC\\|SPC\\|DEL\\)$"
+                              "\\<\\(NUL\\|RET\\|LFD\\|TAB\\|ESC\\|SPC\\|DEL\\)$"
                               word))))
                  (setq key (list (intern word))))
                 ((or (equal word "REM") (string-match "^;;" word))