emacs/man/mark.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985,86,87,93,94,95,1997,2001 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Mark, Killing, Help, Top
@chapter The Mark and the Region
@cindex mark
@cindex setting a mark
@cindex region

  Many Emacs commands operate on an arbitrary contiguous part of the
current buffer.  To specify the text for such a command to operate on,
you set @dfn{the mark} at one end of it, and move point to the other
end.  The text between point and the mark is called @dfn{the region}.
Emacs highlights the region whenever there is one, if you enable
Transient Mark mode (@pxref{Transient Mark}).

  Certain Emacs commands set the mark; other editing commands do not
affect it, so the mark remains where you set it last.  Each Emacs
buffer has its own mark, and setting the mark in one buffer has no
effect on other buffers' marks.  When you return to a buffer that was
current earlier, its mark is at the same place as before.

  The ends of the region are always point and the mark.  It doesn't
matter which of them was put in its current place first, or which one
comes earlier in the text---the region starts from point or the mark
(whichever comes first), and ends at point or the mark (whichever
comes last).  Every time you move point, or set the mark in a new
place, the region changes.

  Many commands that insert text, such as @kbd{C-y} (@code{yank}) and
@kbd{M-x insert-buffer}, position point and the mark at opposite ends
of the inserted text, so that the region consists of the text just
inserted.

  Aside from delimiting the region, the mark is also useful for
remembering a spot that you may want to go back to.  To make this
feature more useful, each buffer remembers 16 previous locations of the
mark in the @dfn{mark ring}.

@menu
* Setting Mark::	Commands to set the mark.
* Transient Mark::	How to make Emacs highlight the region--
			  when there is one.
* Momentary Mark::      Enabling Transient Mark mode momentarily.
* Using Region::	Summary of ways to operate on contents of the region.
* Marking Objects::	Commands to put region around textual units.
* Mark Ring::   	Previous mark positions saved so you can go back there.
* Global Mark Ring::    Previous mark positions in various buffers.
@end menu

@node Setting Mark
@section Setting the Mark

  Here are some commands for setting the mark:

@table @kbd
@item C-@key{SPC}
Set the mark where point is (@code{set-mark-command}).
@item C-@@
The same.
@item C-x C-x
Interchange mark and point (@code{exchange-point-and-mark}).
@item Drag-Mouse-1
Set point and the mark around the text you drag across.
@item Mouse-3
Set the mark where point is, then move point to where you click
(@code{mouse-save-then-kill}).
@end table

  For example, suppose you wish to convert part of the buffer to
upper case, using the @kbd{C-x C-u} (@code{upcase-region}) command,
which operates on the text in the region.  You can first go to the
beginning of the text to be capitalized, type @kbd{C-@key{SPC}} to put
the mark there, move to the end, and then type @kbd{C-x C-u}.  Or, you
can set the mark at the end of the text, move to the beginning, and then
type @kbd{C-x C-u}.

@kindex C-SPC
@findex set-mark-command
  The most common way to set the mark is with the @kbd{C-@key{SPC}} command
(@code{set-mark-command}).  This sets the mark where point is.  Then you
can move point away, leaving the mark behind.

  There are two ways to set the mark with the mouse.  You can drag mouse
button one across a range of text; that puts point where you release the
mouse button, and sets the mark at the other end of that range.  Or you
can click mouse button three, which sets the mark at point (like
@kbd{C-@key{SPC}}) and then moves point (like @kbd{Mouse-1}).  Both of
these methods copy the region into the kill ring in addition to setting
the mark; that gives behavior consistent with other window-driven
applications, but if you don't want to modify the kill ring, you must
use keyboard commands to set the mark.  @xref{Mouse Commands}.

@kindex C-x C-x
@findex exchange-point-and-mark
  Ordinary terminals have only one cursor, so there is no way for Emacs
to show you where the mark is located.  You have to remember.  The usual
solution to this problem is to set the mark and then use it soon, before
you forget where it is.  Alternatively, you can see where the mark is
with the command @kbd{C-x C-x} (@code{exchange-point-and-mark}) which
puts the mark where point was and point where the mark was.  The extent
of the region is unchanged, but the cursor and point are now at the
previous position of the mark.  In Transient Mark mode, this command
also reactivates the mark.

  @kbd{C-x C-x} is also useful when you are satisfied with the position
of point but want to move the other end of the region (where the mark
is); do @kbd{C-x C-x} to put point at that end of the region, and then
move it.  Using @kbd{C-x C-x} a second time, if necessary, puts the mark at
the new position with point back at its original position.

  For more facilities that allow you to go to previously set marks, see
@ref{Mark Ring}.

@kindex C-@@
  There is no such character as @kbd{C-@key{SPC}} in ASCII; when you
type @key{SPC} while holding down @key{CTRL}, what you get on most
ordinary terminals is the character @kbd{C-@@}.  This key is actually
bound to @code{set-mark-command}.  But unless you are unlucky enough to
have a terminal where typing @kbd{C-@key{SPC}} does not produce
@kbd{C-@@}, you might as well think of this character as
@kbd{C-@key{SPC}}.  Under X, @kbd{C-@key{SPC}} is actually a distinct
character, but its binding is still @code{set-mark-command}.

@node Transient Mark
@section Transient Mark Mode
@cindex mode, Transient Mark
@cindex Transient Mark mode
@cindex highlighting region
@cindex region highlighting

  On a terminal that supports colors, Emacs has the ability to
highlight the current region.  But normally it does not.  Why not?

  Once you have set the mark in a buffer, there is @emph{always} a
region in that buffer.  This is because every command that sets the
mark also activates it, and nothing ever deactivates it.  Highlighting
the region all the time would be a nuisance.  So normally Emacs
highlights the region only immediately after you have selected one
with the mouse.

  If you want region highlighting, you can use Transient Mark mode.
This is a more rigid mode of operation in which the region always
``lasts'' only until you use it; you explicitly must set up a region
for each command that uses one.  In Transient Mark mode, most of the
time there is no region; therefore, highlighting the region when it
exists is useful and not annoying.  When Transient Mark mode is
enabled, Emacs always highlights the region whenever there is a
region.

@findex transient-mark-mode
  To enable Transient Mark mode, type @kbd{M-x transient-mark-mode}.
This command toggles the mode; you can use the same command to turn
the mode off again.

  Here are the details of Transient Mark mode:

@itemize @bullet
@item
To set the mark, type @kbd{C-@key{SPC}} (@code{set-mark-command}).
This makes the mark active and thus begins highlighting of the region.
As you move point, you will see the highlighted region grow and
shrink.

@item 
The mouse commands for specifying the mark also make it active.  So do
keyboard commands whose purpose is to specify a region, including
@kbd{M-@@}, @kbd{C-M-@@}, @kbd{M-h}, @kbd{C-M-h}, @kbd{C-x C-p}, and
@kbd{C-x h}.

@item
You can tell that the mark is active because the region is highlighted.

@item
When the mark is active, you can execute commands that operate on the
region, such as killing, indenting, or writing to a file.

@item
Any change to the buffer, such as inserting or deleting a character,
deactivates the mark.  This means any subsequent command that operates
on a region will get an error and refuse to operate.  You can make the
region active again by typing @kbd{C-x C-x}.

@item
Quitting with @kbd{C-g} deactivates the mark.

@item
Commands like @kbd{M->} and @kbd{C-s}, that ``leave the mark behind'' in
addition to some other primary purpose, do not activate the new mark.
You can activate the new region by executing @kbd{C-x C-x}
(@code{exchange-point-and-mark}).

@item
@kbd{C-s} when the mark is active does not alter the mark.

@item
Some commands operate on the region if a region is active.  For
instance, @kbd{C-x u} in Transient Mark mode operates on the region,
when there is a region.  (Outside Transient Mark mode, you must type
@kbd{C-u C-x u} if you want it to operate on the region.)
@xref{Undo}.  Other commands that act this way are identified in their
own documentation.
@end itemize

  The highlighting of the region uses the @code{region} face; you can
customize the appearance of the highlighted region by changing this
face.  @xref{Face Customization}.

@vindex highlight-nonselected-windows
  When multiple windows show the same buffer, they can have different
regions, because they can have different values of point (though they
all share one common mark position).  Ordinarily, only the selected
window highlights its region (@pxref{Windows}).  However, if the
variable @code{highlight-nonselected-windows} is non-@code{nil}, then
each window highlights its own region (provided that Transient Mark mode
is enabled and the mark in the window's buffer is active).

@vindex mark-even-if-inactive
  If the variable @code{mark-even-if-inactive} is non-@code{nil} in
Transient Mark mode, then commands can use the mark and the region
even when it is inactive.  Region highlighting appears and disappears
just as it normally does in Transient Mark mode, but the mark doesn't
really go away when the highlighting disappears, so you can still use
region commands.

@cindex Zmacs mode
  Transient Mark mode is also sometimes known as ``Zmacs mode''
because the Zmacs editor on the MIT Lisp Machine handled the mark in a
similar way.

@node Momentary Mark
@section Using Transient Mark Mode Momentarily

  If you don't like Transient Mark mode in general, you might still
want to use it once in a while.  To do this, type @kbd{C-@key{SPC}
C-@key{SPC}} or @kbd{C-u C-x C-x}.  These commands set or activate the
mark, and enable Transient Mark mode only until the mark is
deactivated.

@table @kbd
@item C-@key{SPC} C-@key{SPC}
@kindex C-@key{SPC} C-@key{SPC}
Set the mark at point (like plain @kbd{C-@key{SPC}}), and enable
Transient Mark mode just once until the mark is deactivated.  (This is
not really a separate command; you are using the @kbd{C-@key{SPC}}
command twice.)

@item C-u C-x C-x
@kindex C-u C-x C-x
Activate the mark without changing it, enable Transient Mark mode just
once until the mark is deactivated.  (This is the @kbd{C-x C-x} command,
@code{exchange-point-and-mark}, with a prefix argument.)
@end table

  One of the secondary features of Transient Mark mode is that certain
commands operate on the region when there is an active region.  If you
don't use Transient Mark mode, the region once set never becomes
inactive, so there is no way these commands to make such a
distinction.  Enabling Transient Mark mode momentarily gives you a way
to use these commands on the region.

  The other way momentarily use of Transient Mark mode is useful
is that it highlights the region for the time being.

@node Using Region
@section Operating on the Region

@cindex operations on a marked region
  Once you have a region and the mark is active, here are some of the
ways you can operate on the region:

@itemize @bullet
@item
Kill it with @kbd{C-w} (@pxref{Killing}).
@item
Save it in a register with @kbd{C-x r s} (@pxref{Registers}).
@item
Save it in a buffer or a file (@pxref{Accumulating Text}).
@item
Convert case with @kbd{C-x C-l} or @kbd{C-x C-u} (@pxref{Case}).
@item
Indent it with @kbd{C-x @key{TAB}} or @kbd{C-M-\} (@pxref{Indentation}).
@item
Fill it as text with @kbd{M-x fill-region} (@pxref{Filling}).
@item
Print hardcopy with @kbd{M-x print-region} (@pxref{Hardcopy}).
@item
Evaluate it as Lisp code with @kbd{M-x eval-region} (@pxref{Lisp Eval}).
@end itemize

  Most commands that operate on the text in the region have the word
@code{region} in their names.

@node Marking Objects
@section Commands to Mark Textual Objects

@cindex marking sections of text
  Here are the commands for placing point and the mark around a textual
object such as a word, list, paragraph or page.

@table @kbd
@item M-@@
Set mark after end of next word (@code{mark-word}).  This command and
the following one do not move point.
@item C-M-@@
Set mark after end of following balanced expression (@code{mark-sexp}).
@item M-h
Put region around current paragraph (@code{mark-paragraph}).
@item C-M-h
Put region around current defun (@code{mark-defun}).
@item C-x h
Put region around the entire buffer (@code{mark-whole-buffer}).
@item C-x C-p
Put region around current page (@code{mark-page}).
@end table

@kbd{M-@@} (@code{mark-word}) puts the mark at the end of the next
word, while @kbd{C-M-@@} (@code{mark-sexp}) puts it at the end of the
next balanced expression (@pxref{Expressions}).  These commands handle
arguments just like @kbd{M-f} and @kbd{C-M-f}.  If you repeat these
commands, the region is extended.  For example, you can type either
@kbd{C-u 2 M-@@} or @kbd{M-@@ M-@@} to mark the next two words.

@kindex C-x h
@findex mark-whole-buffer
   Other commands set both point and mark, to delimit an object in the
buffer.  For example, @kbd{M-h} (@code{mark-paragraph}) moves point to
the beginning of the paragraph that surrounds or follows point, and
puts the mark at the end of that paragraph (@pxref{Paragraphs}).  It
prepares the region so you can indent, case-convert, or kill a whole
paragraph.  With prefix argument, if the argument's value is positive,
@kbd{M-h} marks that many paragraphs starting with the one surrounding
point.  If the prefix argument is @minus{}@var{n}, @kbd{M-h} also
marks @var{n} paragraphs, running back form the one surrounding point.
In that last case, point moves forward to the end of that paragraph,
and the mark goes at the start of the region.  The @kbd{M-h} command
also supports the extension of the region, similar to @kbd{M-@@} and
@kbd{C-M-@@}.

  @kbd{C-M-h} (@code{mark-defun}) similarly puts point before, and the
mark after, the current (or following) major top-level definition, or
defun (@pxref{Moving by Defuns}).  (Currently it only marks one defun,
but repeating it marks more defuns, like for @kbd{M-@@}.)  @kbd{C-x
C-p} (@code{mark-page}) puts point before the current page, and mark
at the end (@pxref{Pages}).  The mark goes after the terminating page
delimiter (to include it in the region), while point goes after the
preceding page delimiter (to exclude it).  A numeric argument
specifies a later page (if positive) or an earlier page (if negative)
instead of the current page.

  Finally, @kbd{C-x h} (@code{mark-whole-buffer}) sets up the entire
buffer as the region, by putting point at the beginning and the mark at
the end.

  In Transient Mark mode, all of these commands activate the mark.

@node Mark Ring
@section The Mark Ring

@kindex C-u C-SPC
@cindex mark ring
@kindex C-u C-@@
  Aside from delimiting the region, the mark is also useful for
remembering a spot that you may want to go back to.  To make this
feature more useful, each buffer remembers 16 previous locations of the
mark, in the @dfn{mark ring}.  Commands that set the mark also push the
old mark onto this ring.  To return to a marked location, use @kbd{C-u
C-@key{SPC}} (or @kbd{C-u C-@@}); this is the command
@code{set-mark-command} given a numeric argument.  It moves point to
where the mark was, and restores the mark from the ring of former
marks.

  If you repeat the character @kbd{C-@key{SPC}}, after typing @kbd{C-u
C-@key{SPC}}, each repetition moves point to a previous mark position
from the ring.  The mark positions you move through in this way are
not lost; they go to the end of the ring.

  Each buffer has its own mark ring.  All editing commands use the current
buffer's mark ring.  In particular, @kbd{C-u C-@key{SPC}} always stays in
the same buffer.

  Many commands that can move long distances, such as @kbd{M-<}
(@code{beginning-of-buffer}), start by setting the mark and saving the
old mark on the mark ring.  This is to make it easier for you to move
back later.  Searches set the mark if they move point.  You can tell
when a command sets the mark because it displays @samp{Mark set} in the
echo area.

  If you want to move back to the same place over and over, the mark
ring may not be convenient enough.  If so, you can record the position
in a register for later retrieval (@pxref{RegPos,, Saving Positions in
Registers}).

@vindex mark-ring-max
  The variable @code{mark-ring-max} specifies the maximum number of
entries to keep in the mark ring.  If that many entries exist and
another one is pushed, the earliest one in the list is discarded.  Repeating
@kbd{C-u C-@key{SPC}} cycles through the positions currently in the
ring.

@vindex mark-ring
  The variable @code{mark-ring} holds the mark ring itself, as a list of
marker objects, with the most recent first.  This variable is local in
every buffer.

@node Global Mark Ring
@section The Global Mark Ring
@cindex global mark ring

  In addition to the ordinary mark ring that belongs to each buffer,
Emacs has a single @dfn{global mark ring}.  It records a sequence of
buffers in which you have recently set the mark, so you can go back
to those buffers.

  Setting the mark always makes an entry on the current buffer's mark
ring.  If you have switched buffers since the previous mark setting, the
new mark position makes an entry on the global mark ring also.  The
result is that the global mark ring records a sequence of buffers that
you have been in, and, for each buffer, a place where you set the mark.

@kindex C-x C-@key{SPC}
@findex pop-global-mark
  The command @kbd{C-x C-@key{SPC}} (@code{pop-global-mark}) jumps to
the buffer and position of the latest entry in the global ring.  It also
rotates the ring, so that successive uses of @kbd{C-x C-@key{SPC}} take
you to earlier and earlier buffers.