Don't bind 'C-x 6' to '2C-mode-map' globally by default.

* lisp/textmodes/two-column.el: Don't autoload global setting of
"\C-x6" to 2C-command.

* lisp/ldefs-boot.el: Update to remove setting "\C-x6" to 2C-command.

* doc/emacs/commands.texi (Keys):
* doc/emacs/text.texi (Two-Column):
* doc/lispref/keymaps.texi (Prefix Keys):
* doc/lispref/maps.texi (Standard Keymaps):
Unbind 'C-x 6' from '2C-mode-map'.

doc/emacs/commands.texi

@@ -118,13 +118,12 @@ C-k} is two key sequences, not one.
   By default, the prefix keys in Emacs are @kbd{C-c}, @kbd{C-h},
 @kbd{C-x}, @kbd{C-x @key{RET}}, @kbd{C-x @@}, @kbd{C-x a}, @kbd{C-x
 n}, @kbd{C-x r}, @kbd{C-x v}, @kbd{C-x 4}, @kbd{C-x 5}, @kbd{C-x 6},
-@key{ESC}, @kbd{M-g}, and @kbd{M-o}.  (@key{F1} and @key{F2} are
-aliases for @kbd{C-h} and @kbd{C-x 6}.)  This list is not cast in
-stone; if you customize Emacs, you can make new prefix keys.  You
-could even eliminate some of the standard ones, though this is not
-recommended for most users; for example, if you remove the prefix
-definition of @kbd{C-x 4}, then @kbd{C-x 4 C-f} becomes an invalid key
-sequence.  @xref{Key Bindings}.
+@key{ESC}, @kbd{M-g}, @kbd{M-o} and @key{F2}.  (@key{F1} is an alias
+for @kbd{C-h}.)  This list is not cast in stone; if you customize
+Emacs, you can make new prefix keys.  You could even eliminate some of
+the standard ones, though this is not recommended for most users; for
+example, if you remove the prefix definition of @kbd{C-x 4}, then
+@kbd{C-x 4 C-f} becomes an invalid key sequence.  @xref{Key Bindings}.
 
   Typing the help character (@kbd{C-h} or @key{F1}) after a prefix key
 displays a list of the commands starting with that prefix.  The sole

doc/emacs/text.texi

@@ -2870,9 +2870,8 @@ of text.  It uses two side-by-side windows, each showing its own
 buffer.  There are three ways to enter two-column mode:
 
 @table @asis
-@item @kbd{@key{F2} 2} or @kbd{C-x 6 2}
+@item @kbd{@key{F2} 2}
 @kindex F2 2
-@kindex C-x 6 2
 @findex 2C-two-columns
 Enter two-column mode with the current buffer on the left, and on the
 right, a buffer whose name is based on the current buffer's name
@@ -2883,9 +2882,8 @@ changed.
 This command is appropriate when the current buffer is empty or contains
 just one column and you want to add another column.
 
-@item @kbd{@key{F2} s} or @kbd{C-x 6 s}
+@item @kbd{@key{F2} s}
 @kindex F2 s
-@kindex C-x 6 s
 @findex 2C-split
 Split the current buffer, which contains two-column text, into two
 buffers, and display them side by side (@code{2C-split}).  The current
@@ -2898,21 +2896,19 @@ This command is appropriate when you have a buffer that already contains
 two-column text, and you wish to separate the columns temporarily.
 
 @item @kbd{@key{F2} b @var{buffer} @key{RET}}
-@itemx @kbd{C-x 6 b @var{buffer} @key{RET}}
 @kindex F2 b
-@kindex C-x 6 b
 @findex 2C-associate-buffer
 Enter two-column mode using the current buffer as the left-hand buffer,
 and using buffer @var{buffer} as the right-hand buffer
 (@code{2C-associate-buffer}).
 @end table
 
-  @kbd{@key{F2} s} or @kbd{C-x 6 s} looks for a column separator, which
-is a string that appears on each line between the two columns.  You can
-specify the width of the separator with a numeric argument to
-@kbd{@key{F2} s}; that many characters, before point, constitute the
-separator string.  By default, the width is 1, so the column separator
-is the character before point.
+  @kbd{@key{F2} s} looks for a column separator, which is a string
+that appears on each line between the two columns.  You can specify
+the width of the separator with a numeric argument to @kbd{@key{F2}
+s}; that many characters, before point, constitute the separator
+string.  By default, the width is 1, so the column separator is the
+character before point.
 
   When a line has the separator at the proper place, @kbd{@key{F2} s}
 puts the text after the separator into the right-hand buffer, and
@@ -2924,25 +2920,22 @@ mode: write it in the left-hand buffer, and put an empty line in the
 right-hand buffer.)
 
 @kindex F2 RET
-@kindex C-x 6 RET
 @findex 2C-newline
-  The command @kbd{@key{F2} @key{RET}} or @kbd{C-x 6 @key{RET}}
-(@code{2C-newline}) inserts a newline in each of the two buffers at
-corresponding positions.  This is the easiest way to add a new line to
-the two-column text while editing it in split buffers.
+  The command @kbd{@key{F2} @key{RET}} (@code{2C-newline}) inserts
+a newline in each of the two buffers at corresponding positions.
+This is the easiest way to add a new line to the two-column text while
+editing it in split buffers.
 
 @kindex F2 1
-@kindex C-x 6 1
 @findex 2C-merge
   When you have edited both buffers as you wish, merge them with
-@kbd{@key{F2} 1} or @kbd{C-x 6 1} (@code{2C-merge}).  This copies the
+@kbd{@key{F2} 1} (@code{2C-merge}).  This copies the
 text from the right-hand buffer as a second column in the other buffer.
 To go back to two-column editing, use @kbd{@key{F2} s}.
 
 @kindex F2 d
-@kindex C-x 6 d
 @findex 2C-dissociate
-  Use @kbd{@key{F2} d} or @kbd{C-x 6 d} to dissociate the two buffers,
-leaving each as it stands (@code{2C-dissociate}).  If the other buffer,
-the one not current when you type @kbd{@key{F2} d}, is empty,
-@kbd{@key{F2} d} kills it.
+  Use @kbd{@key{F2} d} to dissociate the two buffers, leaving each as
+it stands (@code{2C-dissociate}).  If the other buffer, the one not
+current when you type @kbd{@key{F2} d}, is empty, @kbd{@key{F2} d}
+kills it.

doc/lispref/keymaps.texi

@@ -545,8 +545,8 @@ key.
 
 @item
 @cindex @kbd{C-x 6}
-@vindex 2C-mode-map
-@code{2C-mode-map} is the global keymap used for the @kbd{C-x 6} prefix
+@vindex ctl-x-6-map
+@code{ctl-x-6-map} is the global keymap used for the @kbd{C-x 6} prefix
 key.
 
 @item

doc/lispref/maps.texi

@@ -21,7 +21,7 @@ keymaps, @pxref{Keymaps}.
 @c Don't add xrefs to things covered in {Keymaps}.
 @table @code
 @item 2C-mode-map
-A sparse keymap for subcommands of the prefix @kbd{C-x 6}.@*
+A sparse keymap for subcommands of the prefix @key{F2}.@*
 @xref{Two-Column,, Two-Column Editing, emacs, The GNU Emacs Manual}.
 
 @item abbrev-map
@@ -42,6 +42,9 @@ A sparse keymap for subcommands of the prefix @kbd{C-x 4}.
 @item ctl-x-5-map
 A sparse keymap for subcommands of the prefix @kbd{C-x 5}.
 
+@item ctl-x-6-map
+A sparse keymap for subcommands of the prefix @kbd{C-x 6}.
+
 @item ctl-x-map
 A full keymap for @kbd{C-x} commands.
 

etc/NEWS

@@ -2106,6 +2106,11 @@ immediately.  Type 'M-x so-long-commentary' for full documentation.
 
 * Incompatible Lisp Changes in Emacs 27.1
 
+---
+** Two-column mode provides its C-x 6 prefix map only after loading
+two-column.el.  Its prefix key F2 is still available globally
+along with C-x 6 used by the tab commands globally.
+
 ---
 ** Incomplete destructive splicing support has been removed.
 Support for Common Lisp style destructive splicing (",.") was

lisp/ldefs-boot.el

@@ -34138,7 +34138,6 @@ resumed later.
 ;;;;;;  0 0))
 ;;; Generated autoloads from textmodes/two-column.el
  (autoload '2C-command "two-column" () t 'keymap)
- (global-set-key "\C-x6" '2C-command)
  (global-set-key [f2] '2C-command)
 
 (autoload '2C-two-columns "two-column" "\

lisp/textmodes/two-column.el

@@ -184,7 +184,9 @@ minus this value."
 ;; This one is for historical reasons and simple keyboards, it is not
 ;; at all mnemonic.  All usual sequences containing 2 were used, and
 ;; f2 could not be set up in a standard way under Emacs 18.
-;;;###autoload (global-set-key "\C-x6" '2C-command)
+;; This prefix is bound only after loading this package
+;; to not conflict with the C-x 6 prefix used by tab commands.
+(global-set-key "\C-x6" '2C-command)
 
 ;;;###autoload (global-set-key [f2] '2C-command)