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201/NMODE Manual (The Mark and the Region) Page 10-1
202/10. The Mark and the Region
201/In general, a command which processes an arbitrary part of the buffer must
know where to start and where to stop. In NMODE, such commands usually
operate on the text between point and 202/the mark201/. This range of text is called
202/the region201/. To specify a region, you set point to one end of it and mark at
the other. It doesn't matter which one is set first chronologically, or which
one comes earlier in the text. Here are some commands for setting the mark:
C-@ Set the mark where point is.
C-Space The same.
C-X C-X Interchange mark and point.
M-@ Set mark after end of next word. This command and the
following three do not move point.
C-M-@ Set mark after end of next Lisp form.
C-< Set mark at beginning of buffer.
C-> Set mark at end of buffer.
M-H Put region around current paragraph.
C-M-H Put region around current Lisp defun.
C-X H Put region around entire buffer.
For example, if you wish to convert part of the buffer to all upper-case,
you can use the C-X C-U command, which operates on the text in the region.
You can first go to the beginning of the text to be capitalized, put the mark
there, move to the end, and then type C-X C-U. Or, you can set the mark
at the end of the text, move to the beginning, and then type C-X C-U. C-X
C-U runs the function 203/uppercase-region-command201/, whose name signifies that
the region, or everything between point and the mark, is to be capitalized.
The most common way to set the mark is with the C-@ command or the
C-Space command (203/set-mark-command201/). They set the mark where point is.
Then you can move point away, leaving the mark behind.
It isn't actually possible to type C-Space on non-Meta keyboards. Yet on
many terminals the command appears to work anyway! This is because trying
to type a Control-Space on those terminals actually sends the character C-@,
which means the same thing as C-Space. A few keyboards just send a Space.
If you have one of them, you type C-@, or customize your NMODE.
Since terminals have only one cursor, there is no way for NMODE 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. But you can see where the mark is with the command C-X C-X
(203/exchange-point-and-mark201/) 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 location of the mark.
C-X C-X is also useful when you are satisfied with the location of point but
want to move the mark; do C-X C-X to put point there and then you can
move it. A second use of C-X C-X, if necessary, puts the mark at the new
location with point back at its original location.
If you insert or delete before the mark, the mark may drift through the
201/Page 10-2 NMODE Manual (The Mark and the Region)
text. If the buffer contains "FOO BAR" and the mark is before the "B",
then if you delete the "F" the mark will be before the "A". This is an
unfortunate result of the simple way the mark is implemented. It is best not
to delete or insert at places above the mark until you are finished using it
and don't care where it drifts to.
202/10.1 Commands to Mark Textual Objects
201/There are commands for placing the mark on the other side of a certain
object such as a word or a list, without having to move there first. M-@
(203/mark-word-command201/) puts the mark at the end of the next word, while
C-M-@ (203/mark-form-command201/) puts it at the end of the next s-expression.
C-> (203/mark-end-command201/) puts the mark at the end of the buffer, while C-<
(203/mark-beginning-command201/) puts it at the beginning. These characters allow
you to save a little typing or redisplay, sometimes.
Other commands set both point and mark, to delimit an object in the buffer.
M-H (203/mark-paragraph-command201/) puts point at the beginning of the paragraph
it was inside of (or before), and puts the mark at the end. M-H does all
that's necessary if you wish to case-convert or kill a whole paragraph.
C-M-H (203/mark-defun-command201/) similarly puts point before and the mark after
the current or next defun. Finally, C-X H (203/mark-whole-buffer-command201/)
makes the region the entire buffer by putting point at the beginning and the
mark at the end.
202/10.2 The Ring of Marks
201/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,
NMODE remembers 16 previous locations of the mark for each buffer. Most
commands that set the mark push the old mark onto this stack. To return to
a marked location, use C-U C-@ (or C-U C-Space). This moves point to
where the mark was, and restores the mark from the stack of former marks.
So repeated use of this command moves point to all of the old marks on the
stack, one by one. Since the stack is actually a ring, enough uses of C-U
C-@ bring point back to where it was originally. Insertion and deletion can
cause the saved marks to drift, but they will still be good for this purpose
because they are unlikely to drift very far.
Some commands whose primary purpose is to move point a great distance
take advantage of the stack of marks to give you a way to undo the
command. The best example is M-<, which moves to the beginning of the
buffer. It sets the mark first, so that you can use C-U C-@ or C-X C-X to
go back to where you were.