Each buffer has a special marker, which is designated the mark. When a buffer is newly created, this marker exists but does not point anywhere; this means that the mark doesn’t exist in that buffer yet. Subsequent commands can set the mark.
The mark specifies a position to bound a range of text for many
commands, such as kill-region and indent-rigidly. These
commands typically act on the text between point and the mark, which
is called the region. If you are writing a command that
operates on the region, don’t examine the mark directly; instead, use
interactive with the ‘r’ specification. This provides the
values of point and the mark as arguments to the command in an
interactive call, but permits other Lisp programs to specify arguments
explicitly. See Code Characters for interactive.
Some commands set the mark as a side-effect. Commands should do
this only if it has a potential use to the user, and never for their
own internal purposes. For example, the replace-regexp command
sets the mark to the value of point before doing any replacements,
because this enables the user to move back there conveniently after
the replace is finished.
Once the mark exists in a buffer, it normally never ceases to
exist. However, it may become inactive, if Transient Mark mode
is enabled. The buffer-local variable mark-active, if
non-nil, means that the mark is active. A command can call the
function deactivate-mark to deactivate the mark directly, or it
can request deactivation of the mark upon return to the editor command
loop by setting the variable deactivate-mark to a
non-nil value.
If Transient Mark mode is enabled, certain editing commands that normally apply to text near point, apply instead to the region when the mark is active. This is the main motivation for using Transient Mark mode. (Another is that this enables highlighting of the region when the mark is active. See Emacs Display.)
In addition to the mark, each buffer has a mark ring which is a
list of markers containing previous values of the mark. When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring. The variable mark-ring-max specifies the
maximum number of entries in the mark ring; once the list becomes this
long, adding a new element deletes the last element.
There is also a separate global mark ring, but that is used only in a few particular user-level commands, and is not relevant to Lisp programming. So we do not describe it here.
This function returns the current buffer’s mark position as an integer,
or nil if no mark has ever been set in this buffer.
If Transient Mark mode is enabled, and mark-even-if-inactive is
nil, mark signals an error if the mark is inactive.
However, if force is non-nil, then mark disregards
inactivity of the mark, and returns the mark position (or nil)
anyway.
This function returns the marker that represents the current buffer’s mark. It is not a copy, it is the marker used internally. Therefore, changing this marker’s position will directly affect the buffer’s mark. Don’t do that unless that is the effect you want.
(setq m (mark-marker))
⇒ #<marker at 3420 in markers.texi>
(set-marker m 100)
⇒ #<marker at 100 in markers.texi>
(mark-marker)
⇒ #<marker at 100 in markers.texi>
Like any marker, this marker can be set to point at any buffer you like. If you make it point at any buffer other than the one of which it is the mark, it will yield perfectly consistent, but rather odd, results. We recommend that you not do it!
This function sets the mark to position, and activates the mark. The old value of the mark is not pushed onto the mark ring.
Please note: Use this function only if you want the user to
see that the mark has moved, and you want the previous mark position to
be lost. Normally, when a new mark is set, the old one should go on the
mark-ring. For this reason, most applications should use
push-mark and pop-mark, not set-mark.
Novice Emacs Lisp programmers often try to use the mark for the wrong purposes. The mark saves a location for the user’s convenience. An editing command should not alter the mark unless altering the mark is part of the user-level functionality of the command. (And, in that case, this effect should be documented.) To remember a location for internal use in the Lisp program, store it in a Lisp variable. For example:
(let ((beg (point))) (forward-line 1) (delete-region beg (point))).
This function sets the current buffer’s mark to position, and
pushes a copy of the previous mark onto mark-ring. If
position is nil, then the value of point is used.
The function push-mark normally does not activate the
mark. To do that, specify t for the argument activate.
A ‘Mark set’ message is displayed unless nomsg is
non-nil.
This function pops off the top element of mark-ring and makes
that mark become the buffer’s actual mark. This does not move point in
the buffer, and it does nothing if mark-ring is empty. It
deactivates the mark.
This variable, if non-nil, enables Transient Mark mode. In
Transient Mark mode, every buffer-modifying primitive sets
deactivate-mark. As a consequence, most commands that modify
the buffer also deactivate the mark.
When Transient Mark mode is enabled and the mark is active, many
commands that normally apply to the text near point instead apply to
the region. Such commands should use the function use-region-p
to test whether they should operate on the region. See The Region.
Lisp programs can set transient-mark-mode to non-nil,
non-t values to enable Transient Mark mode temporarily. If the
value is lambda, Transient Mark mode is automatically turned
off after any action, such as buffer modification, that would normally
deactivate the mark. If the value is (only . oldval),
then transient-mark-mode is set to the value oldval after
any subsequent command that moves point and is not shift-translated
(see shift-translation), or after any other
action that would normally deactivate the mark. (Marking a region
with the mouse will temporarily enable transient-mark-mode in
this way.)
If this is non-nil, Lisp programs and the Emacs user can use the
mark even when it is inactive. This option affects the behavior of
Transient Mark mode. When the option is non-nil, deactivation of
the mark turns off region highlighting, but commands that use the mark
behave as if the mark were still active.
If an editor command sets this variable non-nil, then the editor
command loop deactivates the mark after the command returns (if
Transient Mark mode is enabled). All the primitives that change the
buffer set deactivate-mark, to deactivate the mark when the
command is finished. Setting this variable makes it buffer-local.
To write Lisp code that modifies the buffer without causing
deactivation of the mark at the end of the command, bind
deactivate-mark to nil around the code that does the
modification. For example:
(let (deactivate-mark) (insert " "))
If Transient Mark mode is enabled or force is non-nil,
this function deactivates the mark and runs the normal hook
deactivate-mark-hook. Otherwise, it does nothing.
The mark is active when this variable is non-nil. This
variable is always buffer-local in each buffer. Do not use the
value of this variable to decide whether a command that normally
operates on text near point should operate on the region instead. Use
the function use-region-p for that (see The Region).
These normal hooks are run, respectively, when the mark becomes active
and when it becomes inactive. The hook activate-mark-hook is
also run when the region is reactivated, for instance after using a
command that switches back to a buffer that has an active mark.
This function implements the shift-selection behavior of
point-motion commands. See Shift Selection in The GNU Emacs
Manual. It is called automatically by the Emacs command loop
whenever a command with a ‘^’ character in its interactive
spec is invoked, before the command itself is executed
(see ^).
If shift-select-mode is non-nil and the current command
was invoked via shift translation (see shift-translation), this function sets the mark and temporarily
activates the region, unless the region was already temporarily
activated in this way. Otherwise, if the region has been activated
temporarily, it deactivates the mark and restores the variable
transient-mark-mode to its earlier value.
The value of this buffer-local variable is the list of saved former marks of the current buffer, most recent first.
mark-ring
⇒ (#<marker at 11050 in markers.texi>
#<marker at 10832 in markers.texi>
…)
The value of this variable is the maximum size of mark-ring. If
more marks than this are pushed onto the mark-ring,
push-mark discards an old mark when it adds a new one.
When Delete Selection mode (see Delete Selection in The GNU Emacs Manual) is enabled, commands that operate on the
active region (a.k.a. “selection”) behave slightly differently.
This works by adding the function delete-selection-pre-hook to
the pre-command-hook (see Command Loop Overview). That function
calls delete-selection-helper to delete the selection as
appropriate for the command. If you want to adapt a command to Delete
Selection mode, put the delete-selection property on the
function’s symbol (see Accessing Symbol Properties); commands that don’t have
this property on their symbol won’t delete the selection. This
property can have one of several values to tailor the behavior to what
the command is supposed to do; see the doc strings of
delete-selection-pre-hook and delete-selection-helper
for the details.