Transient Mark Mode
On a terminal that supports colors, Emacs can highlight the current
region. But normally it does not. Why not?
Highlighting the region whenever it exists would not be desirable in
Emacs, because once you have set a mark, there is always a
region (in that buffer). And 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.
You can turn on region highlighting by enabling Transient Mark mode.
This is a more rigid mode of operation in which the region "lasts"
only temporarily, so you 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.
To enable Transient Mark mode, type M-x transient-mark-mode.
This command toggles the mode, so you can repeat the command to turn off
the mode.
Here are the details of Transient Mark mode:
- To set the mark, type C-<SPC> (
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.
- The mouse commands for specifying the mark also make it active. So do
keyboard commands whose purpose is to specify a region, including
M-@, C-M-@, M-h, C-M-h, C-x C-p, and
C-x h.
- When the mark is active, you can execute commands that operate on the
region, such as killing, indenting, or writing to a file.
- 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 C-x C-x.
- Commands like M-> and 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 C-x C-x
(
exchange-point-and-mark).
- C-s when the mark is active does not alter the mark.
- Quitting with C-g deactivates the mark.
- Some commands operate on the region whenever it is active. For
instance, C-x u in Transient Mark mode operates on the region
when there is a region. Outside Transient Mark mode, you must type
C-u C-x u if you want it to operate on the region.
See Undo. Other commands that act this way are identified
in their own documentation.
The highlighting of the region uses the region face; you can
customize the appearance of the highlighted region by changing this
face. See Face Customization.
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 (see Windows). However, if the
variable highlight-nonselected-windows is non-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).
When Transient Mark mode is not enabled, every command that sets the
mark also activates it, and nothing ever deactivates it.
If the variable mark-even-if-inactive is non-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.
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.
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