One special marker in each buffer is designated the mark. It
records a position for the user for the sake of commands such as
indent-rigidly. Lisp programs should set
the mark only to values that have a potential use to the user, and never
for their own internal purposes. For example, the
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.
Many commands are designed so that when called interactively they
operate on the text between point and the mark. If you are writing such
a command, 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 section Code Characters for
Each buffer has its own value of the mark that is independent of the value of the mark in other buffers. When a buffer is created, the mark exists but does not point anywhere. We consider this state as "the absence of a mark in that buffer."
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 variable
mark-active, which is always buffer-local
in all buffers, indicates whether the mark is active: non-
means yes. A command can request deactivation of the mark upon return
to the editor command loop by setting
deactivate-mark to a
nil value (but this causes deactivation only if Transient
Mark mode is enabled).
The main motivation for using Transient Mark mode is that this mode also enables highlighting of the region when the mark is active. See section 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.
If the mark is inactive,
mark normally signals an error.
However, if force is non-
mark returns the
mark position anyway--or
nil, if the mark is not yet set for
(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. We don't recommend that you make it point at any buffer other than the one of which it is the mark. If you do, it will yield perfectly consistent, but rather odd, results.
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
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))).
mark-ring. If position is
nil, then the value of point is used.
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
mark-ringand makes that mark become the buffer's actual mark. This does not move point in the buffer, and it does nothing if
mark-ringis empty. It deactivates the mark.
The return value is not meaningful.
nilenables Transient Mark mode, in which every buffer-modifying primitive sets
deactivate-mark. The consequence of this is that commands that modify the buffer normally make the mark inactive.
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.
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.
nil. This variable is always buffer-local in each buffer.
activate-mark-hookis also run at the end of a command if the mark is active and it is possible that the region may have changed.
mark-ring => (#<marker at 11050 in markers.texi> #<marker at 10832 in markers.texi> ...)
mark-ring. If more marks than this are pushed onto the
push-markdiscards an old mark when it adds a new one.
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