Narrowing means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the accessible portion of the buffer.
Narrowing is specified with two buffer positions, which become the beginning and end of the accessible portion. For most editing commands and primitives, these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion. Note that narrowing does not alter actual buffer positions (see Point); it only determines which positions are considered the accessible portion of the buffer. Most functions refuse to operate on text that is outside the accessible portion.
Commands for saving buffers are unaffected by narrowing; they save the entire buffer regardless of any narrowing.
If you need to display in a single buffer several very different types of text, consider using an alternative facility described in Swapping Text Between Two Buffers.
This function sets the accessible portion of the current buffer to start at start and end at end. Both arguments should be character positions.
In an interactive call, start and end are set to the bounds of the current region (point and the mark, with the smallest first).
However, when the narrowing has been set by with-restriction with
a label argument (see below), narrow-to-region can be used only
within the limits of that narrowing. If start or end are
outside these limits, the corresponding limit set by
with-restriction is used instead. To gain access to other
portions of the buffer, use without-restriction with the same
label.
This function sets the accessible portion of the current buffer to
include just the current page. An optional first argument
move-count non-nil means to move forward or backward by
move-count pages and then narrow to one page. The variable
page-delimiter specifies where pages start and end
(see Standard Regular Expressions Used in Editing).
In an interactive call, move-count is set to the numeric prefix argument.
This function cancels any narrowing in the current buffer, so that the entire contents are accessible. This is called widening. It is equivalent to the following expression:
(narrow-to-region 1 (1+ (buffer-size)))
However, when a narrowing has been set by with-restriction with a
label argument (see below), the limits set by with-restriction
are restored, instead of canceling the narrowing. To gain access to
other portions of the buffer, use without-restriction with the
same label.
This function returns non-nil if the buffer is narrowed, and
nil otherwise.
This special form saves the current bounds of the accessible portion,
evaluates the body forms, and finally restores the saved bounds,
thus restoring the same state of narrowing (or absence thereof) formerly
in effect. The state of narrowing is restored even in the event of an
abnormal exit via throw or error (see Nonlocal Exits).
Therefore, this construct is a clean way to narrow a buffer temporarily.
This construct also saves and restores the narrowings that were set by
with-restriction with a label argument (see below).
The value returned by save-restriction is that returned by the
last form in body, or nil if no body forms were given.
Caution: it is easy to make a mistake when using the
save-restriction construct. Read the entire description here
before you try it.
If body changes the current buffer, save-restriction still
restores the restrictions on the original buffer (the buffer whose
restrictions it saved from), but it does not restore the identity of the
current buffer.
save-restriction does not restore point; use
save-excursion for that. If you use both save-restriction
and save-excursion together, save-excursion should come
first (on the outside). Otherwise, the old point value would be
restored with temporary narrowing still in effect. If the old point
value were outside the limits of the temporary narrowing, this would
fail to restore it accurately.
Here is a simple example of correct use of save-restriction:
---------- Buffer: foo ---------- This is the contents of foo This is the contents of foo This is the contents of foo∗ ---------- Buffer: foo ----------
(save-excursion
(save-restriction
(goto-char 1)
(forward-line 2)
(narrow-to-region 1 (point))
(goto-char (point-min))
(replace-string "foo" "bar")))
---------- Buffer: foo ----------
This is the contents of bar
This is the contents of bar
This is the contents of foo∗
---------- Buffer: foo ----------
This special form saves the current bounds of the accessible portion of the buffer, sets the accessible portion to start at start and end at end, evaluates the body forms, and restores the saved bounds. In that case it is equivalent to
(save-restriction (narrow-to-region start end) body)
When the optional argument label, which is evaluated to get the
label to use and must yield a non-nil value, is present, the
narrowing is labeled. A labeled narrowing differs from a
non-labeled one in several ways:
narrow-to-region
and widen can be used only within the start and end
limits.
with-restriction and gain
access to other portions of the buffer, use without-restriction
with the same label argument. (Another way to gain access to
other portions of the buffer is to use an indirect buffer
(see Indirect Buffers).)
If you use with-restriction with the optional label
argument, we recommend documenting the label in the doc strings
of the functions which use it, so that other Lisp programs your code
calls could lift the labeled narrowing if and when it needs.
This special form saves the current bounds of the accessible portion of the buffer, widens the buffer, evaluates the body forms, and restores the saved bounds. In that case it is equivalent to
(save-restriction (widen) body)
When the optional argument label is present, the narrowing set
by with-restriction with the same label argument is
lifted.