32. Text
This chapter describes the functions that deal with the text in a
buffer. Most examine, insert, or delete text in the current buffer,
often operating at point or on text adjacent to point. Many are
interactive. All the functions that change the text provide for undoing
the changes (see section 32.9 Undo).
Many text-related functions operate on a region of text defined by two
buffer positions passed in arguments named start and end.
These arguments should be either markers (see section 31. Markers) or numeric
character positions (see section 30. Positions). The order of these arguments
does not matter; it is all right for start to be the end of the
region and end the beginning. For example, (delete-region 1
10) and (delete-region 10 1) are equivalent. An
args-out-of-range error is signaled if either start or
end is outside the accessible portion of the buffer. In an
interactive call, point and the mark are used for these arguments.
Throughout this chapter, "text" refers to the characters in the
buffer, together with their properties (when relevant). Keep in mind
that point is always between two characters, and the cursor appears on
the character after point.
32.1 Examining Text Near Point
Many functions are provided to look at the characters around point.
Several simple functions are described here. See also looking-at
in 34.3 Regular Expression Searching.
- Function: char-after &optional position
- This function returns the character in the current buffer at (i.e.,
immediately after) position position. If position is out of
range for this purpose, either before the beginning of the buffer, or at
or beyond the end, then the value is
nil. The default for
position is point.
In the following example, assume that the first character in the
buffer is `@':
| | (char-to-string (char-after 1))
=> "@"
|
- Function: char-before &optional position
- This function returns the character in the current buffer immediately
before position position. If position is out of range for
this purpose, either before the beginning of the buffer, or at or beyond
the end, then the value is
nil. The default for
position is point.
- Function: following-char
- This function returns the character following point in the current
buffer. This is similar to
(char-after (point)). However, if
point is at the end of the buffer, then following-char returns 0.
Remember that point is always between characters, and the terminal
cursor normally appears over the character following point. Therefore,
the character returned by following-char is the character the
cursor is over.
In this example, point is between the `a' and the `c'.
| | ---------- Buffer: foo ----------
Gentlemen may cry ``Pea-!-ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------
(char-to-string (preceding-char))
=> "a"
(char-to-string (following-char))
=> "c"
|
- Function: preceding-char
- This function returns the character preceding point in the current
buffer. See above, under
following-char, for an example. If
point is at the beginning of the buffer, preceding-char returns
0.
- Function: bobp
- This function returns
t if point is at the beginning of the
buffer. If narrowing is in effect, this means the beginning of the
accessible portion of the text. See also point-min in
30.1 Point.
- Function: eobp
- This function returns
t if point is at the end of the buffer.
If narrowing is in effect, this means the end of accessible portion of
the text. See also point-max in See section 30.1 Point.
- Function: bolp
- This function returns
t if point is at the beginning of a line.
See section 30.2.4 Motion by Text Lines. The beginning of the buffer (or of its accessible
portion) always counts as the beginning of a line.
- Function: eolp
- This function returns
t if point is at the end of a line. The
end of the buffer (or of its accessible portion) is always considered
the end of a line.
32.2 Examining Buffer Contents
This section describes two functions that allow a Lisp program to
convert any portion of the text in the buffer into a string.
- Function: buffer-substring start end
- This function returns a string containing a copy of the text of the
region defined by positions start and end in the current
buffer. If the arguments are not positions in the accessible portion of
the buffer,
buffer-substring signals an args-out-of-range
error.
It is not necessary for start to be less than end; the
arguments can be given in either order. But most often the smaller
argument is written first.
If the text being copied has any text properties, these are copied into
the string along with the characters they belong to. See section 32.19 Text Properties. However, overlays (see section 38.9 Overlays) in the buffer and
their properties are ignored, not copied.
| | ---------- Buffer: foo ----------
This is the contents of buffer foo
---------- Buffer: foo ----------
(buffer-substring 1 10)
=> "This is t"
(buffer-substring (point-max) 10)
=> "he contents of buffer foo
"
|
- Function: buffer-substring-no-properties start end
- This is like
buffer-substring, except that it does not copy text
properties, just the characters themselves. See section 32.19 Text Properties.
- Function: buffer-string
- This function returns the contents of the entire accessible portion of
the current buffer as a string. It is equivalent to
| | (buffer-substring (point-min) (point-max))
|
| | ---------- Buffer: foo ----------
This is the contents of buffer foo
---------- Buffer: foo ----------
(buffer-string)
=> "This is the contents of buffer foo
"
|
- Function: thing-at-point thing
- Return the thing around or next to point, as a string.
The argument thing is a symbol which specifies a kind of syntactic
entity. Possibilities include symbol, list, sexp,
defun, filename, url, word, sentence,
whitespace, line, page, and others.
| | ---------- Buffer: foo ----------
Gentlemen may cry ``Pea-!-ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------
(thing-at-point 'word)
=> "Peace"
(thing-at-point 'line)
=> "Gentlemen may cry ``Peace! Peace!,''\n"
(thing-at-point 'whitespace)
=> nil
|
32.3 Comparing Text
This function lets you compare portions of the text in a buffer, without
copying them into strings first.
- Function: compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
- This function lets you compare two substrings of the same buffer or two
different buffers. The first three arguments specify one substring,
giving a buffer and two positions within the buffer. The last three
arguments specify the other substring in the same way. You can use
nil for buffer1, buffer2, or both to stand for the
current buffer.
The value is negative if the first substring is less, positive if the
first is greater, and zero if they are equal. The absolute value of
the result is one plus the index of the first differing characters
within the substrings.
This function ignores case when comparing characters
if case-fold-search is non-nil. It always ignores
text properties.
Suppose the current buffer contains the text `foobarbar
haha!rara!'; then in this example the two substrings are `rbar '
and `rara!'. The value is 2 because the first substring is greater
at the second character.
| | (compare-buffer-substrings nil 6 11 nil 16 21)
=> 2
|
32.4 Inserting Text
Insertion means adding new text to a buffer. The inserted text
goes at point--between the character before point and the character
after point. Some insertion functions leave point before the inserted
text, while other functions leave it after. We call the former
insertion after point and the latter insertion before point.
Insertion relocates markers that point at positions after the
insertion point, so that they stay with the surrounding text
(see section 31. Markers). When a marker points at the place of insertion,
insertion may or may not relocate the marker, depending on the marker's
insertion type (see section 31.5 Marker Insertion Types). Certain special
functions such as insert-before-markers relocate all such markers
to point after the inserted text, regardless of the markers' insertion
type.
Insertion functions signal an error if the current buffer is
read-only or if they insert within read-only text.
These functions copy text characters from strings and buffers along
with their properties. The inserted characters have exactly the same
properties as the characters they were copied from. By contrast,
characters specified as separate arguments, not part of a string or
buffer, inherit their text properties from the neighboring text.
The insertion functions convert text from unibyte to multibyte in
order to insert in a multibyte buffer, and vice versa--if the text
comes from a string or from a buffer. However, they do not convert
unibyte character codes 128 through 255 to multibyte characters, not
even if the current buffer is a multibyte buffer. See section 33.2 Converting Text Representations.
- Function: insert &rest args
- This function inserts the strings and/or characters args into the
current buffer, at point, moving point forward. In other words, it
inserts the text before point. An error is signaled unless all
args are either strings or characters. The value is
nil.
- Function: insert-before-markers &rest args
- This function inserts the strings and/or characters args into the
current buffer, at point, moving point forward. An error is signaled
unless all args are either strings or characters. The value is
nil.
This function is unlike the other insertion functions in that it
relocates markers initially pointing at the insertion point, to point
after the inserted text. If an overlay begins the insertion point, the
inserted text falls outside the overlay; if a nonempty overlay ends at
the insertion point, the inserted text falls inside that overlay.
- Function: insert-char character &optional count inherit
- This function inserts count instances of character into the
current buffer before point. The argument count should be a
number (
nil means 1), and character must be a character.
The value is nil.
This function does not convert unibyte character codes 128 through 255
to multibyte characters, not even if the current buffer is a multibyte
buffer. See section 33.2 Converting Text Representations.
If inherit is non-nil, then the inserted characters inherit
sticky text properties from the two characters before and after the
insertion point. See section 32.19.6 Stickiness of Text Properties.
- Function: insert-buffer-substring from-buffer-or-name &optional start end
- This function inserts a portion of buffer from-buffer-or-name
(which must already exist) into the current buffer before point. The
text inserted is the region from start and end. (These
arguments default to the beginning and end of the accessible portion of
that buffer.) This function returns
nil.
In this example, the form is executed with buffer `bar' as the
current buffer. We assume that buffer `bar' is initially empty.
| | ---------- Buffer: foo ----------
We hold these truths to be self-evident, that all
---------- Buffer: foo ----------
(insert-buffer-substring "foo" 1 20)
=> nil
---------- Buffer: bar ----------
We hold these truth-!-
---------- Buffer: bar ----------
|
See section 32.19.6 Stickiness of Text Properties, for other insertion functions that inherit
text properties from the nearby text in addition to inserting it.
Whitespace inserted by indentation functions also inherits text
properties.
32.5 User-Level Insertion Commands
This section describes higher-level commands for inserting text,
commands intended primarily for the user but useful also in Lisp
programs.
- Command: insert-buffer from-buffer-or-name
- This command inserts the entire contents of from-buffer-or-name
(which must exist) into the current buffer after point. It leaves
the mark after the inserted text. The value is
nil.
- Command: self-insert-command count
-
This command inserts the last character typed; it does so count
times, before point, and returns
nil. Most printing characters
are bound to this command. In routine use, self-insert-command
is the most frequently called function in Emacs, but programs rarely use
it except to install it on a keymap.
In an interactive call, count is the numeric prefix argument.
This command calls auto-fill-function whenever that is
non-nil and the character inserted is in the table
auto-fill-chars (see section 32.14 Auto Filling).
This command performs abbrev expansion if Abbrev mode is enabled and
the inserted character does not have word-constituent
syntax. (See section 36. Abbrevs and Abbrev Expansion, and 35.2.1 Table of Syntax Classes.)
This is also responsible for calling blink-paren-function when
the inserted character has close parenthesis syntax (see section 38.14 Blinking Parentheses).
Do not try substituting your own definition of
self-insert-command for the standard one. The editor command
loop handles this function specially.
- Command: newline &optional number-of-newlines
- This command inserts newlines into the current buffer before point.
If number-of-newlines is supplied, that many newline characters
are inserted.
This function calls auto-fill-function if the current column
number is greater than the value of fill-column and
number-of-newlines is nil. Typically what
auto-fill-function does is insert a newline; thus, the overall
result in this case is to insert two newlines at different places: one
at point, and another earlier in the line. newline does not
auto-fill if number-of-newlines is non-nil.
This command indents to the left margin if that is not zero.
See section 32.12 Margins for Filling.
The value returned is nil. In an interactive call, count
is the numeric prefix argument.
- Command: split-line
- This command splits the current line, moving the portion of the line
after point down vertically so that it is on the next line directly
below where it was before. Whitespace is inserted as needed at the
beginning of the lower line, using the
indent-to function.
split-line returns the position of point.
Programs hardly ever use this function.
- Variable: overwrite-mode
- This variable controls whether overwrite mode is in effect. The value
should be
overwrite-mode-textual, overwrite-mode-binary,
or nil. overwrite-mode-textual specifies textual
overwrite mode (treats newlines and tabs specially), and
overwrite-mode-binary specifies binary overwrite mode (treats
newlines and tabs like any other characters).
32.6 Deleting Text
Deletion means removing part of the text in a buffer, without saving
it in the kill ring (see section 32.8 The Kill Ring). Deleted text can't be
yanked, but can be reinserted using the undo mechanism (see section 32.9 Undo).
Some deletion functions do save text in the kill ring in some special
cases.
All of the deletion functions operate on the current buffer, and all
return a value of nil.
- Command: erase-buffer
- This function deletes the entire text of the current buffer, leaving it
empty. If the buffer is read-only, it signals a
buffer-read-only
error; if some of the text in it is read-only, it signals a
text-read-only error. Otherwise, it deletes the text without
asking for any confirmation. It returns nil.
Normally, deleting a large amount of text from a buffer inhibits further
auto-saving of that buffer "because it has shrunk". However,
erase-buffer does not do this, the idea being that the future
text is not really related to the former text, and its size should not
be compared with that of the former text.
- Command: delete-region start end
- This command deletes the text between positions start and
end in the current buffer, and returns
nil. If point was
inside the deleted region, its value afterward is start.
Otherwise, point relocates with the surrounding text, as markers do.
- Function: delete-and-extract-region start end
-
This function deletes the text between positions start and
end in the current buffer, and returns a string containing the
text just deleted.
If point was inside the deleted region, its value afterward is
start. Otherwise, point relocates with the surrounding text, as
markers do.
- Command: delete-char count &optional killp
- This command deletes count characters directly after point, or
before point if count is negative. If killp is
non-
nil, then it saves the deleted characters in the kill ring.
In an interactive call, count is the numeric prefix argument, and
killp is the unprocessed prefix argument. Therefore, if a prefix
argument is supplied, the text is saved in the kill ring. If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.
The value returned is always nil.
- Command: delete-backward-char count &optional killp
-
This command deletes count characters directly before point, or
after point if count is negative. If killp is
non-
nil, then it saves the deleted characters in the kill ring.
In an interactive call, count is the numeric prefix argument, and
killp is the unprocessed prefix argument. Therefore, if a prefix
argument is supplied, the text is saved in the kill ring. If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.
The value returned is always nil.
- Command: backward-delete-char-untabify count &optional killp
-
This command deletes count characters backward, changing tabs
into spaces. When the next character to be deleted is a tab, it is
first replaced with the proper number of spaces to preserve alignment
and then one of those spaces is deleted instead of the tab. If
killp is non-
nil, then the command saves the deleted
characters in the kill ring.
Conversion of tabs to spaces happens only if count is positive.
If it is negative, exactly -count characters after point
are deleted.
In an interactive call, count is the numeric prefix argument, and
killp is the unprocessed prefix argument. Therefore, if a prefix
argument is supplied, the text is saved in the kill ring. If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.
The value returned is always nil.
- User Option: backward-delete-char-untabify-method
- This option specifies how
backward-delete-char-untabify should
deal with whitespace. Possible values include untabify, the
default, meaning convert a tab to many spaces and delete one;
hungry, meaning delete all the whitespace characters before point
with one command, and nil, meaning do nothing special for
whitespace characters.
32.7 User-Level Deletion Commands
This section describes higher-level commands for deleting text,
commands intended primarily for the user but useful also in Lisp
programs.
- Command: delete-horizontal-space
-
This function deletes all spaces and tabs around point. It returns
nil.
In the following examples, we call delete-horizontal-space four
times, once on each line, with point between the second and third
characters on the line each time.
| | ---------- Buffer: foo ----------
I -!-thought
I -!- thought
We-!- thought
Yo-!-u thought
---------- Buffer: foo ----------
(delete-horizontal-space) ; Four times.
=> nil
---------- Buffer: foo ----------
Ithought
Ithought
Wethought
You thought
---------- Buffer: foo ----------
|
- Command: delete-indentation &optional join-following-p
- This function joins the line point is on to the previous line, deleting
any whitespace at the join and in some cases replacing it with one
space. If join-following-p is non-
nil,
delete-indentation joins this line to the following line
instead. The function returns nil.
If there is a fill prefix, and the second of the lines being joined
starts with the prefix, then delete-indentation deletes the
fill prefix before joining the lines. See section 32.12 Margins for Filling.
In the example below, point is located on the line starting
`events', and it makes no difference if there are trailing spaces
in the preceding line.
| | ---------- Buffer: foo ----------
When in the course of human
-!- events, it becomes necessary
---------- Buffer: foo ----------
(delete-indentation)
=> nil
---------- Buffer: foo ----------
When in the course of human-!- events, it becomes necessary
---------- Buffer: foo ----------
|
After the lines are joined, the function fixup-whitespace is
responsible for deciding whether to leave a space at the junction.
- Function: fixup-whitespace
- This function replaces all the whitespace surrounding point with either
one space or no space, according to the context. It returns
nil.
At the beginning or end of a line, the appropriate amount of space is
none. Before a character with close parenthesis syntax, or after a
character with open parenthesis or expression-prefix syntax, no space is
also appropriate. Otherwise, one space is appropriate. See section 35.2.1 Table of Syntax Classes.
In the example below, fixup-whitespace is called the first time
with point before the word `spaces' in the first line. For the
second invocation, point is directly after the `('.
| | ---------- Buffer: foo ----------
This has too many -!-spaces
This has too many spaces at the start of (-!- this list)
---------- Buffer: foo ----------
(fixup-whitespace)
=> nil
(fixup-whitespace)
=> nil
---------- Buffer: foo ----------
This has too many spaces
This has too many spaces at the start of (this list)
---------- Buffer: foo ----------
|
- Command: just-one-space
- This command replaces any spaces and tabs around point with a single
space. It returns
nil.
- Command: delete-blank-lines
- This function deletes blank lines surrounding point. If point is on a
blank line with one or more blank lines before or after it, then all but
one of them are deleted. If point is on an isolated blank line, then it
is deleted. If point is on a nonblank line, the command deletes all
blank lines following it.
A blank line is defined as a line containing only tabs and spaces.
delete-blank-lines returns nil.
32.8 The Kill Ring
Kill functions delete text like the deletion functions, but save
it so that the user can reinsert it by yanking. Most of these
functions have `kill-' in their name. By contrast, the functions
whose names start with `delete-' normally do not save text for
yanking (though they can still be undone); these are "deletion"
functions.
Most of the kill commands are primarily for interactive use, and are
not described here. What we do describe are the functions provided for
use in writing such commands. You can use these functions to write
commands for killing text. When you need to delete text for internal
purposes within a Lisp function, you should normally use deletion
functions, so as not to disturb the kill ring contents.
See section 32.6 Deleting Text.
Killed text is saved for later yanking in the kill ring. This
is a list that holds a number of recent kills, not just the last text
kill. We call this a "ring" because yanking treats it as having
elements in a cyclic order. The list is kept in the variable
kill-ring, and can be operated on with the usual functions for
lists; there are also specialized functions, described in this section,
that treat it as a ring.
Some people think this use of the word "kill" is unfortunate, since
it refers to operations that specifically do not destroy the
entities "killed". This is in sharp contrast to ordinary life, in
which death is permanent and "killed" entities do not come back to
life. Therefore, other metaphors have been proposed. For example, the
term "cut ring" makes sense to people who, in pre-computer days, used
scissors and paste to cut up and rearrange manuscripts. However, it
would be difficult to change the terminology now.
32.8.1 Kill Ring Concepts
The kill ring records killed text as strings in a list, most recent
first. A short kill ring, for example, might look like this:
| | ("some text" "a different piece of text" "even older text")
|
When the list reaches kill-ring-max entries in length, adding a
new entry automatically deletes the last entry.
When kill commands are interwoven with other commands, each kill
command makes a new entry in the kill ring. Multiple kill commands in
succession build up a single kill-ring entry, which would be yanked as a
unit; the second and subsequent consecutive kill commands add text to
the entry made by the first one.
For yanking, one entry in the kill ring is designated the "front" of
the ring. Some yank commands "rotate" the ring by designating a
different element as the "front." But this virtual rotation doesn't
change the list itself--the most recent entry always comes first in the
list.
32.8.2 Functions for Killing
kill-region is the usual subroutine for killing text. Any
command that calls this function is a "kill command" (and should
probably have `kill' in its name). kill-region puts the
newly killed text in a new element at the beginning of the kill ring or
adds it to the most recent element. It determines automatically (using
last-command) whether the previous command was a kill command,
and if so appends the killed text to the most recent entry.
- Command: kill-region start end
- This function kills the text in the region defined by start and
end. The text is deleted but saved in the kill ring, along with
its text properties. The value is always
nil.
In an interactive call, start and end are point and
the mark.
If the buffer or text is read-only, kill-region modifies the kill
ring just the same, then signals an error without modifying the buffer.
This is convenient because it lets the user use a series of kill
commands to copy text from a read-only buffer into the kill ring.
- User Option: kill-read-only-ok
- If this option is non-
nil, kill-region does not signal an
error if the buffer or text is read-only. Instead, it simply returns,
updating the kill ring but not changing the buffer.
- Command: copy-region-as-kill start end
- This command saves the region defined by start and end on
the kill ring (including text properties), but does not delete the text
from the buffer. It returns
nil. It also indicates the extent
of the text copied by moving the cursor momentarily, or by displaying a
message in the echo area.
The command does not set this-command to kill-region, so a
subsequent kill command does not append to the same kill ring entry.
Don't call copy-region-as-kill in Lisp programs unless you aim to
support Emacs 18. For newer Emacs versions, it is better to use
kill-new or kill-append instead. See section 32.8.4 Low-Level Kill Ring.
32.8.3 Functions for Yanking
Yanking means reinserting an entry of previously killed text
from the kill ring. The text properties are copied too.
- Command: yank &optional arg
-
This command inserts before point the text in the first entry in the
kill ring. It positions the mark at the beginning of that text, and
point at the end.
If arg is a list (which occurs interactively when the user
types C-u with no digits), then yank inserts the text as
described above, but puts point before the yanked text and puts the mark
after it.
If arg is a number, then yank inserts the argth most
recently killed text--the argth element of the kill ring list.
yank does not alter the contents of the kill ring or rotate it.
It returns nil.
- Command: yank-pop arg
- This command replaces the just-yanked entry from the kill ring with a
different entry from the kill ring.
This is allowed only immediately after a yank or another
yank-pop. At such a time, the region contains text that was just
inserted by yanking. yank-pop deletes that text and inserts in
its place a different piece of killed text. It does not add the deleted
text to the kill ring, since it is already in the kill ring somewhere.
If arg is nil, then the replacement text is the previous
element of the kill ring. If arg is numeric, the replacement is
the argth previous kill. If arg is negative, a more recent
kill is the replacement.
The sequence of kills in the kill ring wraps around, so that after the
oldest one comes the newest one, and before the newest one goes the
oldest.
The return value is always nil.
32.8.4 Low-Level Kill Ring
These functions and variables provide access to the kill ring at a
lower level, but still convenient for use in Lisp programs, because they
take care of interaction with window system selections
(see section 29.18 Window System Selections).
- Function: current-kill n &optional do-not-move
- The function
current-kill rotates the yanking pointer, which
designates the "front" of the kill ring, by n places (from newer
kills to older ones), and returns the text at that place in the ring.
If the optional second argument do-not-move is non-nil,
then current-kill doesn't alter the yanking pointer; it just
returns the nth kill, counting from the current yanking pointer.
If n is zero, indicating a request for the latest kill,
current-kill calls the value of
interprogram-paste-function (documented below) before consulting
the kill ring.
- Function: kill-new string
- This function puts the text string into the kill ring as a new
entry at the front of the ring. It discards the oldest entry if
appropriate. It also invokes the value of
interprogram-cut-function (see below).
- Function: kill-append string before-p
- This function appends the text string to the first entry in the
kill ring. Normally string goes at the end of the entry, but if
before-p is non-
nil, it goes at the beginning. This
function also invokes the value of interprogram-cut-function (see
below).
- Variable: interprogram-paste-function
- This variable provides a way of transferring killed text from other
programs, when you are using a window system. Its value should be
nil or a function of no arguments.
If the value is a function, current-kill calls it to get the
"most recent kill". If the function returns a non-nil value,
then that value is used as the "most recent kill". If it returns
nil, then the first element of kill-ring is used.
The normal use of this hook is to get the window system's primary
selection as the most recent kill, even if the selection belongs to
another application. See section 29.18 Window System Selections.
- Variable: interprogram-cut-function
- This variable provides a way of communicating killed text to other
programs, when you are using a window system. Its value should be
nil or a function of one argument.
If the value is a function, kill-new and kill-append call
it with the new first element of the kill ring as an argument.
The normal use of this hook is to set the window system's primary
selection from the newly killed text. See section 29.18 Window System Selections.
32.8.5 Internals of the Kill Ring
The variable kill-ring holds the kill ring contents, in the
form of a list of strings. The most recent kill is always at the front
of the list.
The kill-ring-yank-pointer variable points to a link in the
kill ring list, whose CAR is the text to yank next. We say it
identifies the "front" of the ring. Moving
kill-ring-yank-pointer to a different link is called
rotating the kill ring. We call the kill ring a "ring" because
the functions that move the yank pointer wrap around from the end of the
list to the beginning, or vice-versa. Rotation of the kill ring is
virtual; it does not change the value of kill-ring.
Both kill-ring and kill-ring-yank-pointer are Lisp
variables whose values are normally lists. The word "pointer" in the
name of the kill-ring-yank-pointer indicates that the variable's
purpose is to identify one element of the list for use by the next yank
command.
The value of kill-ring-yank-pointer is always eq to one
of the links in the kill ring list. The element it identifies is the
CAR of that link. Kill commands, which change the kill ring, also
set this variable to the value of kill-ring. The effect is to
rotate the ring so that the newly killed text is at the front.
Here is a diagram that shows the variable kill-ring-yank-pointer
pointing to the second entry in the kill ring ("some text" "a
different piece of text" "yet older text").
| | kill-ring ---- kill-ring-yank-pointer
| |
| v
| --- --- --- --- --- ---
--> | | |------> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| | -->"yet older text"
| |
| --> "a different piece of text"
|
--> "some text"
|
This state of affairs might occur after C-y (yank)
immediately followed by M-y (yank-pop).
- Variable: kill-ring
- This variable holds the list of killed text sequences, most recently
killed first.
- Variable: kill-ring-yank-pointer
- This variable's value indicates which element of the kill ring is at the
"front" of the ring for yanking. More precisely, the value is a tail
of the value of
kill-ring, and its CAR is the kill string
that C-y should yank.
- User Option: kill-ring-max
- The value of this variable is the maximum length to which the kill
ring can grow, before elements are thrown away at the end. The default
value for
kill-ring-max is 30.
32.9 Undo
Most buffers have an undo list, which records all changes made
to the buffer's text so that they can be undone. (The buffers that
don't have one are usually special-purpose buffers for which Emacs
assumes that undoing is not useful.) All the primitives that modify the
text in the buffer automatically add elements to the front of the undo
list, which is in the variable buffer-undo-list.
- Variable: buffer-undo-list
- This variable's value is the undo list of the current buffer.
A value of
t disables the recording of undo information.
Here are the kinds of elements an undo list can have:
position
- This kind of element records a previous value of point; undoing this
element moves point to position. Ordinary cursor motion does not
make any sort of undo record, but deletion operations use these entries
to record where point was before the command.
(beg . end)
- This kind of element indicates how to delete text that was inserted.
Upon insertion, the text occupied the range beg--end in the
buffer.
(text . position)
- This kind of element indicates how to reinsert text that was deleted.
The deleted text itself is the string text. The place to
reinsert it is
(abs position).
(t high . low)
- This kind of element indicates that an unmodified buffer became
modified. The elements high and low are two integers, each
recording 16 bits of the visited file's modification time as of when it
was previously visited or saved.
primitive-undo uses those
values to determine whether to mark the buffer as unmodified once again;
it does so only if the file's modification time matches those numbers.
(nil property value beg . end)
- This kind of element records a change in a text property.
Here's how you might undo the change:
| | (put-text-property beg end property value)
|
(marker . adjustment)
- This kind of element records the fact that the marker marker was
relocated due to deletion of surrounding text, and that it moved
adjustment character positions. Undoing this element moves
marker - adjustment characters.
nil
- This element is a boundary. The elements between two boundaries are
called a change group; normally, each change group corresponds to
one keyboard command, and undo commands normally undo an entire group as
a unit.
- Function: undo-boundary
- This function places a boundary element in the undo list. The undo
command stops at such a boundary, and successive undo commands undo
to earlier and earlier boundaries. This function returns
nil.
The editor command loop automatically creates an undo boundary before
each key sequence is executed. Thus, each undo normally undoes the
effects of one command. Self-inserting input characters are an
exception. The command loop makes a boundary for the first such
character; the next 19 consecutive self-inserting input characters do
not make boundaries, and then the 20th does, and so on as long as
self-inserting characters continue.
All buffer modifications add a boundary whenever the previous undoable
change was made in some other buffer. This is to ensure that
each command makes a boundary in each buffer where it makes changes.
Calling this function explicitly is useful for splitting the effects of
a command into more than one unit. For example, query-replace
calls undo-boundary after each replacement, so that the user can
undo individual replacements one by one.
- Function: primitive-undo count list
- This is the basic function for undoing elements of an undo list.
It undoes the first count elements of list, returning
the rest of list. You could write this function in Lisp,
but it is convenient to have it in C.
primitive-undo adds elements to the buffer's undo list when it
changes the buffer. Undo commands avoid confusion by saving the undo
list value at the beginning of a sequence of undo operations. Then the
undo operations use and update the saved value. The new elements added
by undoing are not part of this saved value, so they don't interfere with
continuing to undo.
32.10 Maintaining Undo Lists
This section describes how to enable and disable undo information for
a given buffer. It also explains how the undo list is truncated
automatically so it doesn't get too big.
Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled. You can explicitly enable or
disable undo recording with the following two functions, or by setting
buffer-undo-list yourself.
- Command: buffer-enable-undo &optional buffer-or-name
- This command enables recording undo information for buffer
buffer-or-name, so that subsequent changes can be undone. If no
argument is supplied, then the current buffer is used. This function
does nothing if undo recording is already enabled in the buffer. It
returns
nil.
In an interactive call, buffer-or-name is the current buffer.
You cannot specify any other buffer.
- Command: buffer-disable-undo &optional buffer
-
- Command: buffer-flush-undo &optional buffer
-
This function discards the undo list of buffer, and disables
further recording of undo information. As a result, it is no longer
possible to undo either previous changes or any subsequent changes. If
the undo list of buffer is already disabled, this function
has no effect.
This function returns nil.
The name buffer-flush-undo is not considered obsolete, but the
preferred name is buffer-disable-undo.
As editing continues, undo lists get longer and longer. To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set. (For this purpose, the "size"
of an undo list measures the cons cells that make up the list, plus the
strings of deleted text.) Two variables control the range of acceptable
sizes: undo-limit and undo-strong-limit.
- Variable: undo-limit
- This is the soft limit for the acceptable size of an undo list. The
change group at which this size is exceeded is the last one kept.
- Variable: undo-strong-limit
- This is the upper limit for the acceptable size of an undo list. The
change group at which this size is exceeded is discarded itself (along
with all older change groups). There is one exception: the very latest
change group is never discarded no matter how big it is.
32.11 Filling
Filling means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width. Additionally, lines can be justified, which means
inserting spaces to make the left and/or right margins line up
precisely. The width is controlled by the variable fill-column.
For ease of reading, lines should be no longer than 70 or so columns.
You can use Auto Fill mode (see section 32.14 Auto Filling) to fill text
automatically as you insert it, but changes to existing text may leave
it improperly filled. Then you must fill the text explicitly.
Most of the commands in this section return values that are not
meaningful. All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(see section 32.12 Margins for Filling). If the current justification style is
none, the filling functions don't actually do anything.
Several of the filling functions have an argument justify.
If it is non-nil, that requests some kind of justification. It
can be left, right, full, or center, to
request a specific style of justification. If it is t, that
means to use the current justification style for this part of the text
(see current-justification, below). Any other value is treated
as full.
When you call the filling functions interactively, using a prefix
argument implies the value full for justify.
- Command: fill-paragraph justify
-
This command fills the paragraph at or after point. If
justify is non-
nil, each line is justified as well.
It uses the ordinary paragraph motion commands to find paragraph
boundaries. See section `Paragraphs' in The GNU Emacs Manual.
- Command: fill-region start end &optional justify nosqueeze to-eop
- This command fills each of the paragraphs in the region from start
to end. It justifies as well if justify is
non-
nil.
If nosqueeze is non-nil, that means to leave whitespace
other than line breaks untouched. If to-eop is non-nil,
that means to keep filling to the end of the paragraph--or the next hard
newline, if use-hard-newlines is enabled (see below).
The variable paragraph-separate controls how to distinguish
paragraphs. See section 34.8 Standard Regular Expressions Used in Editing.
- Command: fill-individual-paragraphs start end &optional justify citation-regexp
- This command fills each paragraph in the region according to its
individual fill prefix. Thus, if the lines of a paragraph were indented
with spaces, the filled paragraph will remain indented in the same
fashion.
The first two arguments, start and end, are the beginning
and end of the region to be filled. The third and fourth arguments,
justify and citation-regexp, are optional. If
justify is non-nil, the paragraphs are justified as
well as filled. If citation-regexp is non-nil, it means the
function is operating on a mail message and therefore should not fill
the header lines. If citation-regexp is a string, it is used as
a regular expression; if it matches the beginning of a line, that line
is treated as a citation marker.
Ordinarily, fill-individual-paragraphs regards each change in
indentation as starting a new paragraph. If
fill-individual-varying-indent is non-nil, then only
separator lines separate paragraphs. That mode can handle indented
paragraphs with additional indentation on the first line.
- User Option: fill-individual-varying-indent
- This variable alters the action of
fill-individual-paragraphs as
described above.
- Command: fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
- This command considers a region of text as a single paragraph and fills
it. If the region was made up of many paragraphs, the blank lines
between paragraphs are removed. This function justifies as well as
filling when justify is non-
nil.
In an interactive call, any prefix argument requests justification.
If nosqueeze is non-nil, that means to leave whitespace
other than line breaks untouched. If squeeze-after is
non-nil, it specifies a position in the region, and means don't
canonicalize spaces before that position.
In Adaptive Fill mode, this command calls fill-context-prefix to
choose a fill prefix by default. See section 32.13 Adaptive Fill Mode.
- Command: justify-current-line &optional how eop nosqueeze
- This command inserts spaces between the words of the current line so
that the line ends exactly at
fill-column. It returns
nil.
The argument how, if non-nil specifies explicitly the style
of justification. It can be left, right, full,
center, or none. If it is t, that means to do
follow specified justification style (see current-justification,
below). nil means to do full justification.
If eop is non-nil, that means do left-justification if
current-justification specifies full justification. This is used
for the last line of a paragraph; even if the paragraph as a whole is
fully justified, the last line should not be.
If nosqueeze is non-nil, that means do not change interior
whitespace.
- User Option: default-justification
- This variable's value specifies the style of justification to use for
text that doesn't specify a style with a text property. The possible
values are
left, right, full, center, or
none. The default value is left.
- Function: current-justification
- This function returns the proper justification style to use for filling
the text around point.
- User Option: sentence-end-double-space
- If this variable is non-
nil, a period followed by just one space
does not count as the end of a sentence, and the filling functions
avoid breaking the line at such a place.
- Variable: fill-paragraph-function
- This variable provides a way for major modes to override the filling of
paragraphs. If the value is non-
nil, fill-paragraph calls
this function to do the work. If the function returns a non-nil
value, fill-paragraph assumes the job is done, and immediately
returns that value.
The usual use of this feature is to fill comments in programming
language modes. If the function needs to fill a paragraph in the usual
way, it can do so as follows:
| | (let ((fill-paragraph-function nil))
(fill-paragraph arg))
|
- Variable: use-hard-newlines
- If this variable is non-
nil, the filling functions do not delete
newlines that have the hard text property. These "hard
newlines" act as paragraph separators.
32.12 Margins for Filling
- User Option: fill-prefix
- This buffer-local variable specifies a string of text that appears at
the beginning
of normal text lines and should be disregarded when filling them. Any
line that fails to start with the fill prefix is considered the start of
a paragraph; so is any line that starts with the fill prefix followed by
additional whitespace. Lines that start with the fill prefix but no
additional whitespace are ordinary text lines that can be filled
together. The resulting filled lines also start with the fill prefix.
The fill prefix follows the left margin whitespace, if any.
- User Option: fill-column
- This buffer-local variable specifies the maximum width of filled lines.
Its value should be an integer, which is a number of columns. All the
filling, justification, and centering commands are affected by this
variable, including Auto Fill mode (see section 32.14 Auto Filling).
As a practical matter, if you are writing text for other people to
read, you should set fill-column to no more than 70. Otherwise
the line will be too long for people to read comfortably, and this can
make the text seem clumsy.
- Variable: default-fill-column
- The value of this variable is the default value for
fill-column in
buffers that do not override it. This is the same as
(default-value 'fill-column).
The default value for default-fill-column is 70.
- Command: set-left-margin from to margin
- This sets the
left-margin property on the text from from to
to to the value margin. If Auto Fill mode is enabled, this
command also refills the region to fit the new margin.
- Command: set-right-margin from to margin
- This sets the
right-margin property on the text from from
to to to the value margin. If Auto Fill mode is enabled,
this command also refills the region to fit the new margin.
- Function: current-left-margin
- This function returns the proper left margin value to use for filling
the text around point. The value is the sum of the
left-margin
property of the character at the start of the current line (or zero if
none), and the value of the variable left-margin.
- Function: current-fill-column
- This function returns the proper fill column value to use for filling
the text around point. The value is the value of the
fill-column
variable, minus the value of the right-margin property of the
character after point.
- Command: move-to-left-margin &optional n force
- This function moves point to the left margin of the current line. The
column moved to is determined by calling the function
current-left-margin. If the argument n is non-nil,
move-to-left-margin moves forward n-1 lines first.
If force is non-nil, that says to fix the line's
indentation if that doesn't match the left margin value.
- Function: delete-to-left-margin &optional from to
- This function removes left margin indentation from the text between
from and to. The amount of indentation to delete is
determined by calling
current-left-margin. In no case does this
function delete non-whitespace. If from and to are omitted,
they default to the whole buffer.
- Function: indent-to-left-margin
- This is the default
indent-line-function, used in Fundamental
mode, Text mode, etc. Its effect is to adjust the indentation at the
beginning of the current line to the value specified by the variable
left-margin. This may involve either inserting or deleting
whitespace.
- Variable: left-margin
- This variable specifies the base left margin column. In Fundamental
mode, C-j indents to this column. This variable automatically
becomes buffer-local when set in any fashion.
- Variable: fill-nobreak-predicate
- This variable gives major modes a way to specify not to break a line at
certain places. Its value should be a function. This function is
called during filling, with no arguments and with point located at the
place where a break is being considered. If the function returns
non-
nil, then the line won't be broken there.
32.13 Adaptive Fill Mode
Adaptive Fill mode chooses a fill prefix automatically from the text
in each paragraph being filled.
- User Option: adaptive-fill-mode
- Adaptive Fill mode is enabled when this variable is non-
nil.
It is t by default.
- Function: fill-context-prefix from to
- This function implements the heart of Adaptive Fill mode; it chooses a
fill prefix based on the text between from and to. It does
this by looking at the first two lines of the paragraph, based on the
variables described below.
- User Option: adaptive-fill-regexp
- This variable holds a regular expression to control Adaptive Fill mode.
Adaptive Fill mode matches this regular expression against the text
starting after the left margin whitespace (if any) on a line; the
characters it matches are that line's candidate for the fill prefix.
- User Option: adaptive-fill-first-line-regexp
- In a one-line paragraph, if the candidate fill prefix matches this
regular expression, or if it matches
comment-start-skip, then it
is used--otherwise, spaces amounting to the same width are used
instead.
However, the fill prefix is never taken from a one-line paragraph
if it would act as a paragraph starter on subsequent lines.
- User Option: adaptive-fill-function
- You can specify more complex ways of choosing a fill prefix
automatically by setting this variable to a function. The function is
called when
adaptive-fill-regexp does not match, with point after
the left margin of a line, and it should return the appropriate fill
prefix based on that line. If it returns nil, that means it sees
no fill prefix in that line.
32.14 Auto Filling
Auto Fill mode is a minor mode that fills lines automatically as text
is inserted. This section describes the hook used by Auto Fill mode.
For a description of functions that you can call explicitly to fill and
justify existing text, see 32.11 Filling.
Auto Fill mode also enables the functions that change the margins and
justification style to refill portions of the text. See section 32.12 Margins for Filling.
- Variable: auto-fill-function
- The value of this variable should be a function (of no arguments) to be
called after self-inserting a character from the table
auto-fill-chars. It may be nil, in which case nothing
special is done in that case.
The value of auto-fill-function is do-auto-fill when
Auto-Fill mode is enabled. That is a function whose sole purpose is to
implement the usual strategy for breaking a line.
In older Emacs versions, this variable was named auto-fill-hook,
but since it is not called with the standard convention for hooks, it
was renamed to auto-fill-function in version 19.
- Variable: normal-auto-fill-function
- This variable specifies the function to use for
auto-fill-function, if and when Auto Fill is turned on. Major
modes can set buffer-local values for this variable to alter how Auto
Fill works.
- Variable: auto-fill-chars
- A char table of characters which invoke
auto-fill-function when
self-inserted--space and newline in most language environments. They
have an entry t in the table.
32.15 Sorting Text
The sorting functions described in this section all rearrange text in
a buffer. This is in contrast to the function sort, which
rearranges the order of the elements of a list (see section 5.6.3 Functions that Rearrange Lists).
The values returned by these functions are not meaningful.
- Function: sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun
- This function is the general text-sorting routine that subdivides a
buffer into records and then sorts them. Most of the commands in this
section use this function.
To understand how sort-subr works, consider the whole accessible
portion of the buffer as being divided into disjoint pieces called
sort records. The records may or may not be contiguous, but they
must not overlap. A portion of each sort record (perhaps all of it) is
designated as the sort key. Sorting rearranges the records in order by
their sort keys.
Usually, the records are rearranged in order of ascending sort key.
If the first argument to the sort-subr function, reverse,
is non-nil, the sort records are rearranged in order of
descending sort key.
The next four arguments to sort-subr are functions that are
called to move point across a sort record. They are called many times
from within sort-subr.
-
nextrecfun is called with point at the end of a record. This
function moves point to the start of the next record. The first record
is assumed to start at the position of point when
sort-subr is
called. Therefore, you should usually move point to the beginning of
the buffer before calling sort-subr.
This function can indicate there are no more sort records by leaving
point at the end of the buffer.
-
endrecfun is called with point within a record. It moves point to
the end of the record.
-
startkeyfun is called to move point from the start of a record to
the start of the sort key. This argument is optional; if it is omitted,
the whole record is the sort key. If supplied, the function should
either return a non-
nil value to be used as the sort key, or
return nil to indicate that the sort key is in the buffer
starting at point. In the latter case, endkeyfun is called to
find the end of the sort key.
-
endkeyfun is called to move point from the start of the sort key
to the end of the sort key. This argument is optional. If
startkeyfun returns
nil and this argument is omitted (or
nil), then the sort key extends to the end of the record. There
is no need for endkeyfun if startkeyfun returns a
non-nil value.
As an example of sort-subr, here is the complete function
definition for sort-lines:
| | ;; Note that the first two lines of doc string
;; are effectively one line when viewed by a user.
(defun sort-lines (reverse beg end)
"Sort lines in region alphabetically;\
argument means descending order.
Called from a program, there are three arguments:
REVERSE (non-nil means reverse order),\
BEG and END (region to sort).
The variable `sort-fold-case' determines\
whether alphabetic case affects
the sort order.
(interactive "P\nr")
(save-excursion
(save-restriction
(narrow-to-region beg end)
(goto-char (point-min))
(sort-subr reverse 'forward-line 'end-of-line))))
|
Here forward-line moves point to the start of the next record,
and end-of-line moves point to the end of record. We do not pass
the arguments startkeyfun and endkeyfun, because the entire
record is used as the sort key.
The sort-paragraphs function is very much the same, except that
its sort-subr call looks like this:
| | (sort-subr reverse
(function
(lambda ()
(while (and (not (eobp))
(looking-at paragraph-separate))
(forward-line 1))))
'forward-paragraph)
|
Markers pointing into any sort records are left with no useful
position after sort-subr returns.
- User Option: sort-fold-case
- If this variable is non-
nil, sort-subr and the other
buffer sorting functions ignore case when comparing strings.
- Command: sort-regexp-fields reverse record-regexp key-regexp start end
- This command sorts the region between start and end
alphabetically as specified by record-regexp and key-regexp.
If reverse is a negative integer, then sorting is in reverse
order.
Alphabetical sorting means that two sort keys are compared by
comparing the first characters of each, the second characters of each,
and so on. If a mismatch is found, it means that the sort keys are
unequal; the sort key whose character is less at the point of first
mismatch is the lesser sort key. The individual characters are compared
according to their numerical character codes in the Emacs character set.
The value of the record-regexp argument specifies how to divide
the buffer into sort records. At the end of each record, a search is
done for this regular expression, and the text that matches it is taken
as the next record. For example, the regular expression `^.+$',
which matches lines with at least one character besides a newline, would
make each such line into a sort record. See section 34.2 Regular Expressions, for
a description of the syntax and meaning of regular expressions.
The value of the key-regexp argument specifies what part of each
record is the sort key. The key-regexp could match the whole
record, or only a part. In the latter case, the rest of the record has
no effect on the sorted order of records, but it is carried along when
the record moves to its new position.
The key-regexp argument can refer to the text matched by a
subexpression of record-regexp, or it can be a regular expression
on its own.
If key-regexp is:
- `\digit'
- then the text matched by the digitth `\(...\)' parenthesis
grouping in record-regexp is the sort key.
- `\&'
- then the whole record is the sort key.
- a regular expression
- then
sort-regexp-fields searches for a match for the regular
expression within the record. If such a match is found, it is the sort
key. If there is no match for key-regexp within a record then
that record is ignored, which means its position in the buffer is not
changed. (The other records may move around it.)
For example, if you plan to sort all the lines in the region by the
first word on each line starting with the letter `f', you should
set record-regexp to `^.*$' and set key-regexp to
`\<f\w*\>'. The resulting expression looks like this:
| | (sort-regexp-fields nil "^.*$" "\\"
(region-beginning)
(region-end))
|
If you call sort-regexp-fields interactively, it prompts for
record-regexp and key-regexp in the minibuffer.
- Command: sort-lines reverse start end
- This command alphabetically sorts lines in the region between
start and end. If reverse is non-
nil, the sort
is in reverse order.
- Command: sort-paragraphs reverse start end
- This command alphabetically sorts paragraphs in the region between
start and end. If reverse is non-
nil, the sort
is in reverse order.
- Command: sort-pages reverse start end
- This command alphabetically sorts pages in the region between
start and end. If reverse is non-
nil, the sort
is in reverse order.
- Command: sort-fields field start end
- This command sorts lines in the region between start and
end, comparing them alphabetically by the fieldth field
of each line. Fields are separated by whitespace and numbered starting
from 1. If field is negative, sorting is by the
-fieldth field from the end of the line. This command
is useful for sorting tables.
- Command: sort-numeric-fields field start end
- This command sorts lines in the region between start and
end, comparing them numerically by the fieldth field of each
line. The specified field must contain a number in each line of the
region. Fields are separated by whitespace and numbered starting from
1. If field is negative, sorting is by the
-fieldth field from the end of the line. This command
is useful for sorting tables.
- Command: sort-columns reverse &optional beg end
- This command sorts the lines in the region between beg and
end, comparing them alphabetically by a certain range of columns.
The column positions of beg and end bound the range of
columns to sort on.
If reverse is non-nil, the sort is in reverse order.
One unusual thing about this command is that the entire line
containing position beg, and the entire line containing position
end, are included in the region sorted.
Note that sort-columns uses the sort utility program,
and so cannot work properly on text containing tab characters. Use
M-x untabify to convert tabs to spaces before sorting.
32.16 Counting Columns
The column functions convert between a character position (counting
characters from the beginning of the buffer) and a column position
(counting screen characters from the beginning of a line).
These functions count each character according to the number of
columns it occupies on the screen. This means control characters count
as occupying 2 or 4 columns, depending upon the value of
ctl-arrow, and tabs count as occupying a number of columns that
depends on the value of tab-width and on the column where the tab
begins. See section 38.16 Usual Display Conventions.
Column number computations ignore the width of the window and the
amount of horizontal scrolling. Consequently, a column value can be
arbitrarily high. The first (or leftmost) column is numbered 0.
- Function: current-column
- This function returns the horizontal position of point, measured in
columns, counting from 0 at the left margin. The column position is the
sum of the widths of all the displayed representations of the characters
between the start of the current line and point.
For an example of using current-column, see the description of
count-lines in 30.2.4 Motion by Text Lines.
- Function: move-to-column column &optional force
- This function moves point to column in the current line. The
calculation of column takes into account the widths of the
displayed representations of the characters between the start of the
line and point.
If column column is beyond the end of the line, point moves to the
end of the line. If column is negative, point moves to the
beginning of the line.
If it is impossible to move to column column because that is in
the middle of a multicolumn character such as a tab, point moves to the
end of that character. However, if force is non-nil, and
column is in the middle of a tab, then move-to-column
converts the tab into spaces so that it can move precisely to column
column. Other multicolumn characters can cause anomalies despite
force, since there is no way to split them.
The argument force also has an effect if the line isn't long
enough to reach column column; if it is t, that means to
add whitespace at the end of the line to reach that column.
If column is not an integer, an error is signaled.
The return value is the column number actually moved to.
32.17 Indentation
The indentation functions are used to examine, move to, and change
whitespace that is at the beginning of a line. Some of the functions
can also change whitespace elsewhere on a line. Columns and indentation
count from zero at the left margin.
32.17.1 Indentation Primitives
This section describes the primitive functions used to count and
insert indentation. The functions in the following sections use these
primitives. See section 38.10 Width, for related functions.
- Function: current-indentation
- This function returns the indentation of the current line, which is
the horizontal position of the first nonblank character. If the
contents are entirely blank, then this is the horizontal position of the
end of the line.
- Command: indent-to column &optional minimum
- This function indents from point with tabs and spaces until column
is reached. If minimum is specified and non-
nil, then at
least that many spaces are inserted even if this requires going beyond
column. Otherwise the function does nothing if point is already
beyond column. The value is the column at which the inserted
indentation ends.
The inserted whitespace characters inherit text properties from the
surrounding text (usually, from the preceding text only). See section 32.19.6 Stickiness of Text Properties.
- User Option: indent-tabs-mode
- If this variable is non-
nil, indentation functions can insert
tabs as well as spaces. Otherwise, they insert only spaces. Setting
this variable automatically makes it buffer-local in the current buffer.
32.17.2 Indentation Controlled by Major Mode
An important function of each major mode is to customize the TAB
key to indent properly for the language being edited. This section
describes the mechanism of the TAB key and how to control it.
The functions in this section return unpredictable values.
- Variable: indent-line-function
- This variable's value is the function to be used by TAB (and
various commands) to indent the current line. The command
indent-according-to-mode does no more than call this function.
In Lisp mode, the value is the symbol lisp-indent-line; in C
mode, c-indent-line; in Fortran mode, fortran-indent-line.
In Fundamental mode, Text mode, and many other modes with no standard
for indentation, the value is indent-to-left-margin (which is the
default value).
- Command: indent-according-to-mode
- This command calls the function in
indent-line-function to
indent the current line in a way appropriate for the current major mode.
- Command: indent-for-tab-command
- This command calls the function in
indent-line-function to indent
the current line; however, if that function is
indent-to-left-margin, insert-tab is called instead. (That
is a trivial command that inserts a tab character.)
- Command: newline-and-indent
- This function inserts a newline, then indents the new line (the one
following the newline just inserted) according to the major mode.
It does indentation by calling the current indent-line-function.
In programming language modes, this is the same thing TAB does,
but in some text modes, where TAB inserts a tab,
newline-and-indent indents to the column specified by
left-margin.
- Command: reindent-then-newline-and-indent
- This command reindents the current line, inserts a newline at point,
and then indents the new line (the one following the newline just
inserted).
This command does indentation on both lines according to the current
major mode, by calling the current value of indent-line-function.
In programming language modes, this is the same thing TAB does,
but in some text modes, where TAB inserts a tab,
reindent-then-newline-and-indent indents to the column specified
by left-margin.
32.17.3 Indenting an Entire Region
This section describes commands that indent all the lines in the
region. They return unpredictable values.
- Command: indent-region start end to-column
- This command indents each nonblank line starting between start
(inclusive) and end (exclusive). If to-column is
nil, indent-region indents each nonblank line by calling
the current mode's indentation function, the value of
indent-line-function.
If to-column is non-nil, it should be an integer
specifying the number of columns of indentation; then this function
gives each line exactly that much indentation, by either adding or
deleting whitespace.
If there is a fill prefix, indent-region indents each line
by making it start with the fill prefix.
- Variable: indent-region-function
- The value of this variable is a function that can be used by
indent-region as a short cut. It should take two arguments, the
start and end of the region. You should design the function so
that it will produce the same results as indenting the lines of the
region one by one, but presumably faster.
If the value is nil, there is no short cut, and
indent-region actually works line by line.
A short-cut function is useful in modes such as C mode and Lisp mode,
where the indent-line-function must scan from the beginning of
the function definition: applying it to each line would be quadratic in
time. The short cut can update the scan information as it moves through
the lines indenting them; this takes linear time. In a mode where
indenting a line individually is fast, there is no need for a short cut.
indent-region with a non-nil argument to-column has
a different meaning and does not use this variable.
- Command: indent-rigidly start end count
- This command indents all lines starting between start
(inclusive) and end (exclusive) sideways by count columns.
This "preserves the shape" of the affected region, moving it as a
rigid unit. Consequently, this command is useful not only for indenting
regions of unindented text, but also for indenting regions of formatted
code.
For example, if count is 3, this command adds 3 columns of
indentation to each of the lines beginning in the region specified.
In Mail mode, C-c C-y (mail-yank-original) uses
indent-rigidly to indent the text copied from the message being
replied to.
- Function: indent-code-rigidly start end columns &optional nochange-regexp
- This is like
indent-rigidly, except that it doesn't alter lines
that start within strings or comments.
In addition, it doesn't alter a line if nochange-regexp matches at
the beginning of the line (if nochange-regexp is non-nil).
32.17.4 Indentation Relative to Previous Lines
This section describes two commands that indent the current line
based on the contents of previous lines.
- Command: indent-relative &optional unindented-ok
- This command inserts whitespace at point, extending to the same
column as the next indent point of the previous nonblank line. An
indent point is a non-whitespace character following whitespace. The
next indent point is the first one at a column greater than the current
column of point. For example, if point is underneath and to the left of
the first non-blank character of a line of text, it moves to that column
by inserting whitespace.
If the previous nonblank line has no next indent point (i.e., none at a
great enough column position), indent-relative either does
nothing (if unindented-ok is non-nil) or calls
tab-to-tab-stop. Thus, if point is underneath and to the right
of the last column of a short line of text, this command ordinarily
moves point to the next tab stop by inserting whitespace.
The return value of indent-relative is unpredictable.
In the following example, point is at the beginning of the second
line:
| | This line is indented twelve spaces.
-!-The quick brown fox jumped.
|
Evaluation of the expression (indent-relative nil) produces the
following:
| | This line is indented twelve spaces.
-!-The quick brown fox jumped.
|
In this next example, point is between the `m' and `p' of
`jumped':
| | This line is indented twelve spaces.
The quick brown fox jum-!-ped.
|
Evaluation of the expression (indent-relative nil) produces the
following:
| | This line is indented twelve spaces.
The quick brown fox jum -!-ped.
|
- Command: indent-relative-maybe
- This command indents the current line like the previous nonblank line,
by calling
indent-relative with t as the
unindented-ok argument. The return value is unpredictable.
If the previous nonblank line has no indent points beyond the current
column, this command does nothing.
32.17.5 Adjustable "Tab Stops"
This section explains the mechanism for user-specified "tab stops"
and the mechanisms that use and set them. The name "tab stops" is
used because the feature is similar to that of the tab stops on a
typewriter. The feature works by inserting an appropriate number of
spaces and tab characters to reach the next tab stop column; it does not
affect the display of tab characters in the buffer (see section 38.16 Usual Display Conventions). Note that the TAB character as input uses this tab
stop feature only in a few major modes, such as Text mode.
- Command: tab-to-tab-stop
- This command inserts spaces or tabs before point, up to the next tab
stop column defined by
tab-stop-list. It searches the list for
an element greater than the current column number, and uses that element
as the column to indent to. It does nothing if no such element is
found.
- User Option: tab-stop-list
- This variable is the list of tab stop columns used by
tab-to-tab-stops. The elements should be integers in increasing
order. The tab stop columns need not be evenly spaced.
Use M-x edit-tab-stops to edit the location of tab stops
interactively.
32.17.6 Indentation-Based Motion Commands
These commands, primarily for interactive use, act based on the
indentation in the text.
- Command: back-to-indentation
- This command moves point to the first non-whitespace character in the
current line (which is the line in which point is located). It returns
nil.
- Command: backward-to-indentation arg
- This command moves point backward arg lines and then to the
first nonblank character on that line. It returns
nil.
- Command: forward-to-indentation arg
- This command moves point forward arg lines and then to the first
nonblank character on that line. It returns
nil.
32.18 Case Changes
The case change commands described here work on text in the current
buffer. See section 4.8 Case Conversion in Lisp, for case conversion functions that work
on strings and characters. See section 4.9 The Case Table, for how to customize
which characters are upper or lower case and how to convert them.
- Command: capitalize-region start end
- This function capitalizes all words in the region defined by
start and end. To capitalize means to convert each word's
first character to upper case and convert the rest of each word to lower
case. The function returns
nil.
If one end of the region is in the middle of a word, the part of the
word within the region is treated as an entire word.
When capitalize-region is called interactively, start and
end are point and the mark, with the smallest first.
| | ---------- Buffer: foo ----------
This is the contents of the 5th foo.
---------- Buffer: foo ----------
(capitalize-region 1 44)
=> nil
---------- Buffer: foo ----------
This Is The Contents Of The 5th Foo.
---------- Buffer: foo ----------
|
- Command: downcase-region start end
- This function converts all of the letters in the region defined by
start and end to lower case. The function returns
nil.
When downcase-region is called interactively, start and
end are point and the mark, with the smallest first.
- Command: upcase-region start end
- This function converts all of the letters in the region defined by
start and end to upper case. The function returns
nil.
When upcase-region is called interactively, start and
end are point and the mark, with the smallest first.
- Command: capitalize-word count
- This function capitalizes count words after point, moving point
over as it does. To capitalize means to convert each word's first
character to upper case and convert the rest of each word to lower case.
If count is negative, the function capitalizes the
-count previous words but does not move point. The value
is
nil.
If point is in the middle of a word, the part of the word before point
is ignored when moving forward. The rest is treated as an entire word.
When capitalize-word is called interactively, count is
set to the numeric prefix argument.
- Command: downcase-word count
- This function converts the count words after point to all lower
case, moving point over as it does. If count is negative, it
converts the -count previous words but does not move point.
The value is
nil.
When downcase-word is called interactively, count is set
to the numeric prefix argument.
- Command: upcase-word count
- This function converts the count words after point to all upper
case, moving point over as it does. If count is negative, it
converts the -count previous words but does not move point.
The value is
nil.
When upcase-word is called interactively, count is set to
the numeric prefix argument.
32.19 Text Properties
Each character position in a buffer or a string can have a text
property list, much like the property list of a symbol (see section 8.4 Property Lists). The properties belong to a particular character at a
particular place, such as, the letter `T' at the beginning of this
sentence or the first `o' in `foo'---if the same character
occurs in two different places, the two occurrences generally have
different properties.
Each property has a name and a value. Both of these can be any Lisp
object, but the name is normally a symbol. The usual way to access the
property list is to specify a name and ask what value corresponds to it.
If a character has a category property, we call it the
category of the character. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the character.
Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
substring, insert, and buffer-substring.
32.19.1 Examining Text Properties
The simplest way to examine text properties is to ask for the value of
a particular property of a particular character. For that, use
get-text-property. Use text-properties-at to get the
entire property list of a character. See section 32.19.3 Text Property Search Functions, for
functions to examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that
positions in a string start from 0, whereas positions in a buffer start
from 1.
- Function: get-text-property pos prop &optional object
- This function returns the value of the prop property of the
character after position pos in object (a buffer or
string). The argument object is optional and defaults to the
current buffer.
If there is no prop property strictly speaking, but the character
has a category that is a symbol, then get-text-property returns
the prop property of that symbol.
- Function: get-char-property pos prop &optional object
- This function is like
get-text-property, except that it checks
overlays first and then text properties. See section 38.9 Overlays.
The argument object may be a string, a buffer, or a window. If it
is a window, then the buffer displayed in that window is used for text
properties and overlays, but only the overlays active for that window
are considered. If object is a buffer, then all overlays in that
buffer are considered, as well as text properties. If object is a
string, only text properties are considered, since strings never have
overlays.
- Function: text-properties-at position &optional object
- This function returns the entire property list of the character at
position in the string or buffer object. If object is
nil, it defaults to the current buffer.
- Variable: default-text-properties
- This variable holds a property list giving default values for text
properties. Whenever a character does not specify a value for a
property, neither directly nor through a category symbol, the value
stored in this list is used instead. Here is an example:
| | (setq default-text-properties '(foo 69))
;; Make sure character 1 has no properties of its own.
(set-text-properties 1 2 nil)
;; What we get, when we ask, is the default value.
(get-text-property 1 'foo)
=> 69
|
32.19.2 Changing Text Properties
The primitives for changing properties apply to a specified range of
text in a buffer or string. The function set-text-properties
(see end of section) sets the entire property list of the text in that
range; more often, it is useful to add, change, or delete just certain
properties specified by name.
Since text properties are considered part of the contents of the
buffer (or string), and can affect how a buffer looks on the screen, any
change in buffer text properties marks the buffer as modified. Buffer
text property changes are undoable also (see section 32.9 Undo).
- Function: put-text-property start end prop value &optional object
- This function sets the prop property to value for the text
between start and end in the string or buffer object.
If object is
nil, it defaults to the current buffer.
- Function: add-text-properties start end props &optional object
- This function adds or overrides text properties for the text between
start and end in the string or buffer object. If
object is
nil, it defaults to the current buffer.
The argument props specifies which properties to add. It should
have the form of a property list (see section 8.4 Property Lists): a list whose
elements include the property names followed alternately by the
corresponding values.
The return value is t if the function actually changed some
property's value; nil otherwise (if props is nil or
its values agree with those in the text).
For example, here is how to set the comment and face
properties of a range of text:
| | (add-text-properties start end
'(comment t face highlight))
|
- Function: remove-text-properties start end props &optional object
- This function deletes specified text properties from the text between
start and end in the string or buffer object. If
object is
nil, it defaults to the current buffer.
The argument props specifies which properties to delete. It
should have the form of a property list (see section 8.4 Property Lists): a list
whose elements are property names alternating with corresponding values.
But only the names matter--the values that accompany them are ignored.
For example, here's how to remove the face property.
| | (remove-text-properties start end '(face nil))
|
The return value is t if the function actually changed some
property's value; nil otherwise (if props is nil or
if no character in the specified text had any of those properties).
To remove all text properties from certain text, use
set-text-properties and specify nil for the new property
list.
- Function: set-text-properties start end props &optional object
- This function completely replaces the text property list for the text
between start and end in the string or buffer object.
If object is
nil, it defaults to the current buffer.
The argument props is the new property list. It should be a list
whose elements are property names alternating with corresponding values.
After set-text-properties returns, all the characters in the
specified range have identical properties.
If props is nil, the effect is to get rid of all properties
from the specified range of text. Here's an example:
| | (set-text-properties start end nil)
|
The easiest way to make a string with text properties
is with propertize:
- Function: propertize string &rest properties
-
This function returns a copy of string which has the text
properties properties. These properties apply to all the
characters in the string that is returned. Here is an example that
constructs a string with a
face property and a mouse-face
property:
| | (propertize "foo" 'face 'italic
'mouse-face 'bold-italic)
=> #("foo" 0 3 (mouse-face bold-italic face italic))
|
To put different properties on various parts of a string, you can
construct each part with propertize and then combine them with
concat:
| | (concat
(propertize "foo" 'face 'italic
'mouse-face 'bold-italic)
" and "
(propertize "bar" 'face 'italic
'mouse-face 'bold-italic))
=> #("foo and bar"
0 3 (face italic mouse-face bold-italic)
3 8 nil
8 11 (face italic mouse-face bold-italic))
|
See also the function buffer-substring-no-properties
(see section 32.2 Examining Buffer Contents) which copies text from the buffer
but does not copy its properties.
32.19.3 Text Property Search Functions
In typical use of text properties, most of the time several or many
consecutive characters have the same value for a property. Rather than
writing your programs to examine characters one by one, it is much
faster to process chunks of text that have the same property value.
Here are functions you can use to do this. They use eq for
comparing property values. In all cases, object defaults to the
current buffer.
For high performance, it's very important to use the limit
argument to these functions, especially the ones that search for a
single property--otherwise, they may spend a long time scanning to the
end of the buffer, if the property you are interested in does not change.
These functions do not move point; instead, they return a position (or
nil). Remember that a position is always between two characters;
the position returned by these functions is between two characters with
different properties.
- Function: next-property-change pos &optional object limit
- The function scans the text forward from position pos in the
string or buffer object till it finds a change in some text
property, then returns the position of the change. In other words, it
returns the position of the first character beyond pos whose
properties are not identical to those of the character just after
pos.
If limit is non-nil, then the scan ends at position
limit. If there is no property change before that point,
next-property-change returns limit.
The value is nil if the properties remain unchanged all the way
to the end of object and limit is nil. If the value
is non-nil, it is a position greater than or equal to pos.
The value equals pos only when limit equals pos.
Here is an example of how to scan the buffer by chunks of text within
which all properties are constant:
| | (while (not (eobp))
(let ((plist (text-properties-at (point)))
(next-change
(or (next-property-change (point) (current-buffer))
(point-max))))
Process text from point to next-change...
(goto-char next-change)))
|
- Function: next-single-property-change pos prop &optional object limit
- The function scans the text forward from position pos in the
string or buffer object till it finds a change in the prop
property, then returns the position of the change. In other words, it
returns the position of the first character beyond pos whose
prop property differs from that of the character just after
pos.
If limit is non-nil, then the scan ends at position
limit. If there is no property change before that point,
next-single-property-change returns limit.
The value is nil if the property remains unchanged all the way to
the end of object and limit is nil. If the value is
non-nil, it is a position greater than or equal to pos; it
equals pos only if limit equals pos.
- Function: previous-property-change pos &optional object limit
- This is like
next-property-change, but scans back from pos
instead of forward. If the value is non-nil, it is a position
less than or equal to pos; it equals pos only if limit
equals pos.
- Function: previous-single-property-change pos prop &optional object limit
- This is like
next-single-property-change, but scans back from
pos instead of forward. If the value is non-nil, it is a
position less than or equal to pos; it equals pos only if
limit equals pos.
- Function: next-char-property-change pos &optional limit
- This is like
next-property-change except that it considers
overlay properties as well as text properties, and if no change is
found before the end of the buffer, it returns the maximum buffer
position rather than nil (in this sense, it resembles the
corresponding overlay function next-overlay-change, rather than
next-property-change). There is no object operand
because this function operates only on the current buffer. It returns
the next address at which either kind of property changes.
- Function: previous-char-property-change pos &optional limit
- This is like
next-char-property-change, but scans back from
pos instead of forward, and returns the minimum buffer
position if no change is found.
- Function: next-single-char-property-change pos prop &optional object limit
-
This is like
next-single-property-change except that it
considers overlay properties as well as text properties, and if no
change is found before the end of the object, it returns the
maximum valid position in object rather than nil. Unlike
next-char-property-change, this function does have an
object operand; if object is not a buffer, only
text-properties are considered.
- Function: previous-single-char-property-change pos prop &optional object limit
-
This is like
next-single-char-property-change, but scans back
from pos instead of forward, and returns the minimum valid
position in object if no change is found.
- Function: text-property-any start end prop value &optional object
- This function returns non-
nil if at least one character between
start and end has a property prop whose value is
value. More precisely, it returns the position of the first such
character. Otherwise, it returns nil.
The optional fifth argument, object, specifies the string or
buffer to scan. Positions are relative to object. The default
for object is the current buffer.
- Function: text-property-not-all start end prop value &optional object
- This function returns non-
nil if at least one character between
start and end does not have a property prop with value
value. More precisely, it returns the position of the first such
character. Otherwise, it returns nil.
The optional fifth argument, object, specifies the string or
buffer to scan. Positions are relative to object. The default
for object is the current buffer.
32.19.4 Properties with Special Meanings
Here is a table of text property names that have special built-in
meanings. The following sections list a few additional special property
names that control filling and property inheritance. All other names
have no standard meaning, and you can use them as you like.
category
- If a character has a
category property, we call it the
category of the character. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the character.
face
-
You can use the property
face to control the font and color of
text. See section 38.11 Faces, for more information.
In the simplest case, the value is a face name. It can also be a list;
then each element can be any of these possibilities;
See section 23.5 Font Lock Mode, for information on how to update face
properties automatically based on the contents of the text.
mouse-face
-
The property
mouse-face is used instead of face when the
mouse is on or near the character. For this purpose, "near" means
that all text between the character and where the mouse is have the same
mouse-face property value.
fontified
-
This property, if non-
nil, says that text in the buffer has
had faces assigned automatically by a feature such as Font-Lock mode.
See section 38.11.8 Automatic Face Assignment.
display
-
This property activates various features that change the
way text is displayed. For example, it can make text appear taller
or shorter, higher or lower, wider or narrow, or replaced with an image.
See section 38.12 The
display Property.
help-echo
-
If text has a string as its
help-echo property, then when you
move the mouse onto that text, Emacs displays that string in the echo
area, or in the tooltip window.
If the value of the help-echo property is a function, that
function is called with three arguments, window, object and
position and should return a help string or nil for
none. The first argument, window is the window in which
the help was found. The second, object, is the buffer, overlay or
string which had the help-echo property. The position
argument is as follows:
-
If object is a buffer, pos is the position in the buffer
where the
help-echo text property was found.
-
If object is an overlay, that overlay has a
help-echo
property, and pos is the position in the overlay's buffer under
the mouse.
-
If object is a string (an overlay string or a string displayed
with the
display property), pos is the position in that
string under the mouse.
If the value of the help-echo property is neither a function nor
a string, it is evaluated to obtain a help string.
You can alter the way help text is displayed by setting the variable
show-help-function (see Help display).
This feature is used in the mode line and for other active text. It is
available starting in Emacs 21.
local-map
-
You can specify a different keymap for some of the text in a buffer by
means of the
local-map property. The property's value for the
character after point, if non-nil, is used for key lookup instead
of the buffer's local map. If the property value is a symbol, the
symbol's function definition is used as the keymap. See section 22.6 Active Keymaps.
keymap
-
The
keymap property is similar to local-map but overrides the
buffer's local map (and the map specified by the local-map
property) rather than replacing it.
syntax-table
- The
syntax-table property overrides what the syntax table says
about this particular character. See section 35.4 Syntax Properties.
read-only
-
If a character has the property
read-only, then modifying that
character is not allowed. Any command that would do so gets an error,
text-read-only.
Insertion next to a read-only character is an error if inserting
ordinary text there would inherit the read-only property due to
stickiness. Thus, you can control permission to insert next to
read-only text by controlling the stickiness. See section 32.19.6 Stickiness of Text Properties.
Since changing properties counts as modifying the buffer, it is not
possible to remove a read-only property unless you know the
special trick: bind inhibit-read-only to a non-nil value
and then remove the property. See section 27.7 Read-Only Buffers.
invisible
-
A non-
nil invisible property can make a character invisible
on the screen. See section 38.5 Invisible Text, for details.
intangible
-
If a group of consecutive characters have equal and non-
nil
intangible properties, then you cannot place point between them.
If you try to move point forward into the group, point actually moves to
the end of the group. If you try to move point backward into the group,
point actually moves to the start of the group.
When the variable inhibit-point-motion-hooks is non-nil,
the intangible property is ignored.
field
-
Consecutive characters with the same
field property constitute a
field. Some motion functions including forward-word and
beginning-of-line stop moving at a field boundary.
See section 32.19.10 Defining and Using Fields.
modification-hooks
-
If a character has the property
modification-hooks, then its
value should be a list of functions; modifying that character calls all
of those functions. Each function receives two arguments: the beginning
and end of the part of the buffer being modified. Note that if a
particular modification hook function appears on several characters
being modified by a single primitive, you can't predict how many times
the function will be called.
insert-in-front-hooks
insert-behind-hooks
-
The operation of inserting text in a buffer also calls the functions
listed in the
insert-in-front-hooks property of the following
character and in the insert-behind-hooks property of the
preceding character. These functions receive two arguments, the
beginning and end of the inserted text. The functions are called
after the actual insertion takes place.
See also 32.25 Change Hooks, for other hooks that are called
when you change text in a buffer.
point-entered
point-left
-
The special properties
point-entered and point-left
record hook functions that report motion of point. Each time point
moves, Emacs compares these two property values:
-
the
point-left property of the character after the old location,
and
-
the
point-entered property of the character after the new
location.
If these two values differ, each of them is called (if not nil)
with two arguments: the old value of point, and the new one.
The same comparison is made for the characters before the old and new
locations. The result may be to execute two point-left functions
(which may be the same function) and/or two point-entered
functions (which may be the same function). In any case, all the
point-left functions are called first, followed by all the
point-entered functions.
It is possible using char-after to examine characters at various
positions without moving point to those positions. Only an actual
change in the value of point runs these hook functions.
- Variable: inhibit-point-motion-hooks
- When this variable is non-
nil, point-left and
point-entered hooks are not run, and the intangible
property has no effect. Do not set this variable globally; bind it with
let.
- Variable: show-help-function
-
If this variable is non-
nil, it specifies a
function called to display help strings. These may be help-echo
properties, menu help strings (see section 22.12.1.1 Simple Menu Items,
see section 22.12.1.2 Extended Menu Items), or tool bar help strings (see section 22.12.6 Tool bars). The specified function is called with one argument, the help
string to display. Tooltip mode (see section `Tooltips' in The GNU Emacs Manual) provides an example.
32.19.5 Formatted Text Properties
These text properties affect the behavior of the fill commands. They
are used for representing formatted text. See section 32.11 Filling, and
32.12 Margins for Filling.
hard
- If a newline character has this property, it is a "hard" newline.
The fill commands do not alter hard newlines and do not move words
across them. However, this property takes effect only if the variable
use-hard-newlines is non-nil.
right-margin
- This property specifies an extra right margin for filling this part of the
text.
left-margin
- This property specifies an extra left margin for filling this part of the
text.
justification
- This property specifies the style of justification for filling this part
of the text.
32.19.6 Stickiness of Text Properties
Self-inserting characters normally take on the same properties as the
preceding character. This is called inheritance of properties.
In a Lisp program, you can do insertion with inheritance or without,
depending on your choice of insertion primitive. The ordinary text
insertion functions such as insert do not inherit any properties.
They insert text with precisely the properties of the string being
inserted, and no others. This is correct for programs that copy text
from one context to another--for example, into or out of the kill ring.
To insert with inheritance, use the special primitives described in this
section. Self-inserting characters inherit properties because they work
using these primitives.
When you do insertion with inheritance, which properties are
inherited, and from where, depends on which properties are sticky.
Insertion after a character inherits those of its properties that are
rear-sticky. Insertion before a character inherits those of its
properties that are front-sticky. When both sides offer different
sticky values for the same property, the previous character's value
takes precedence.
By default, a text property is rear-sticky but not front-sticky; thus,
the default is to inherit all the properties of the preceding character,
and nothing from the following character.
You can control the stickiness of various text properties with two
specific text properties, front-sticky and rear-nonsticky,
and with the variable text-property-default-nonsticky. You can
use the variable to specify a different default for a given property.
You can use those two text properties to make any specific properties
sticky or nonsticky in any particular part of the text.
If a character's front-sticky property is t, then all
its properties are front-sticky. If the front-sticky property is
a list, then the sticky properties of the character are those whose
names are in the list. For example, if a character has a
front-sticky property whose value is (face read-only),
then insertion before the character can inherit its face property
and its read-only property, but no others.
The rear-nonsticky property works the opposite way. Most
properties are rear-sticky by default, so the rear-nonsticky
property says which properties are not rear-sticky. If a
character's rear-nonsticky property is t, then none of its
properties are rear-sticky. If the rear-nonsticky property is a
list, properties are rear-sticky unless their names are in the
list.
- Variable: text-property-default-nonsticky
-
This variable holds an alist which defines the default rear-stickiness
of various text properties. Each element has the form
(property . nonstickiness), and it defines the
stickiness of a particular text property, property.
If nonstickiness is non-nil, this means that the property
property is rear-nonsticky by default. Since all properties are
front-nonsticky by default, this makes property nonsticky in both
directions by default.
The text properties front-sticky and rear-nonsticky, when
used, take precedence over the default nonstickiness specifed in
text-property-default-nonsticky.
Here are the functions that insert text with inheritance of properties:
- Function: insert-and-inherit &rest strings
- Insert the strings strings, just like the function
insert,
but inherit any sticky properties from the adjoining text.
- Function: insert-before-markers-and-inherit &rest strings
- Insert the strings strings, just like the function
insert-before-markers, but inherit any sticky properties from the
adjoining text.
See section 32.4 Inserting Text, for the ordinary insertion functions which do not
inherit.
32.19.7 Saving Text Properties in Files
You can save text properties in files (along with the text itself),
and restore the same text properties when visiting or inserting the
files, using these two hooks:
- Variable: write-region-annotate-functions
- This variable's value is a list of functions for
write-region to
run to encode text properties in some fashion as annotations to the text
being written in the file. See section 25.4 Writing to Files.
Each function in the list is called with two arguments: the start and
end of the region to be written. These functions should not alter the
contents of the buffer. Instead, they should return lists indicating
annotations to write in the file in addition to the text in the
buffer.
Each function should return a list of elements of the form
(position . string), where position is an
integer specifying the relative position within the text to be written,
and string is the annotation to add there.
Each list returned by one of these functions must be already sorted in
increasing order by position. If there is more than one function,
write-region merges the lists destructively into one sorted list.
When write-region actually writes the text from the buffer to the
file, it intermixes the specified annotations at the corresponding
positions. All this takes place without modifying the buffer.
- Variable: after-insert-file-functions
- This variable holds a list of functions for
insert-file-contents
to call after inserting a file's contents. These functions should scan
the inserted text for annotations, and convert them to the text
properties they stand for.
Each function receives one argument, the length of the inserted text;
point indicates the start of that text. The function should scan that
text for annotations, delete them, and create the text properties that
the annotations specify. The function should return the updated length
of the inserted text, as it stands after those changes. The value
returned by one function becomes the argument to the next function.
These functions should always return with point at the beginning of
the inserted text.
The intended use of after-insert-file-functions is for converting
some sort of textual annotations into actual text properties. But other
uses may be possible.
We invite users to write Lisp programs to store and retrieve text
properties in files, using these hooks, and thus to experiment with
various data formats and find good ones. Eventually we hope users
will produce good, general extensions we can install in Emacs.
We suggest not trying to handle arbitrary Lisp objects as text property
names or values--because a program that general is probably difficult
to write, and slow. Instead, choose a set of possible data types that
are reasonably flexible, and not too hard to encode.
See section 25.12 File Format Conversion, for a related feature.
32.19.8 Lazy Computation of Text Properties
Instead of computing text properties for all the text in the buffer,
you can arrange to compute the text properties for parts of the text
when and if something depends on them.
The primitive that extracts text from the buffer along with its
properties is buffer-substring. Before examining the properties,
this function runs the abnormal hook buffer-access-fontify-functions.
- Variable: buffer-access-fontify-functions
- This variable holds a list of functions for computing text properties.
Before
buffer-substring copies the text and text properties for a
portion of the buffer, it calls all the functions in this list. Each of
the functions receives two arguments that specify the range of the
buffer being accessed. (The buffer itself is always the current
buffer.)
The function buffer-substring-no-properties does not call these
functions, since it ignores text properties anyway.
In order to prevent the hook functions from being called more than
once for the same part of the buffer, you can use the variable
buffer-access-fontified-property.
- Variable: buffer-access-fontified-property
- If this value's variable is non-
nil, it is a symbol which is used
as a text property name. A non-nil value for that text property
means, "the other text properties for this character have already been
computed."
If all the characters in the range specified for buffer-substring
have a non-nil value for this property, buffer-substring
does not call the buffer-access-fontify-functions functions. It
assumes these characters already have the right text properties, and
just copies the properties they already have.
The normal way to use this feature is that the
buffer-access-fontify-functions functions add this property, as
well as others, to the characters they operate on. That way, they avoid
being called over and over for the same text.
32.19.9 Defining Clickable Text
There are two ways to set up clickable text in a buffer.
There are typically two parts of this: to make the text highlight
when the mouse is over it, and to make a mouse button do something
when you click it on that part of the text.
Highlighting is done with the mouse-face text property.
Here is an example of how Dired does it:
| | (condition-case nil
(if (dired-move-to-filename)
(put-text-property (point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'mouse-face 'highlight))
(error nil))
|
The first two arguments to put-text-property specify the
beginning and end of the text.
The usual way to make the mouse do something when you click it
on this text is to define mouse-2 in the major mode's
keymap. The job of checking whether the click was on clickable text
is done by the command definition. Here is how Dired does it:
| | (defun dired-mouse-find-file-other-window (event)
"In dired, visit the file or directory name you click on."
(interactive "e")
(let (file)
(save-excursion
(set-buffer (window-buffer (posn-window (event-end event))))
(save-excursion
(goto-char (posn-point (event-end event)))
(setq file (dired-get-filename))))
(select-window (posn-window (event-end event)))
(find-file-other-window (file-name-sans-versions file t))))
|
The reason for the outer save-excursion construct is to avoid
changing the current buffer; the reason for the inner one is to avoid
permanently altering point in the buffer you click on. In this case,
Dired uses the function dired-get-filename to determine which
file to visit, based on the position found in the event.
Instead of defining a mouse command for the major mode, you can define
a key binding for the clickable text itself, using the keymap
text property:
| | (let ((map (make-sparse-keymap)))
(define-key map [mouse-2] 'operate-this-button)
(put-text-property (point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'keymap map))
|
This method makes it possible to define different commands for various
clickable pieces of text. Also, the major mode definition (or the
global definition) remains available for the rest of the text in the
buffer.
32.19.10 Defining and Using Fields
A field is a range of consecutive characters in the buffer that are
identified by having the same value (comparing with eq) of the
field property (either a text-property or an overlay property).
This section describes special functions that are available for
operating on fields.
You specify a field with a buffer position, pos. We think of
each field as containing a range of buffer positions, so the position
you specify stands for the field containing that position.
When the characters before and after pos are part of the same
field, there is no doubt which field contains pos: the one those
characters both belong to. When pos is at a boundary between
fields, which field it belongs to depends on the stickiness of the
field properties of the two surrounding characters (see section 32.19.6 Stickiness of Text Properties). The field whose property would be inherited by text
inserted at pos is the field that contains pos.
There is an anomalous case where newly inserted text at pos
would not inherit the field property from either side. This
happens if the previous character's field property is not
rear-sticky, and the following character's field property is not
front-sticky. In this case, pos belongs to neither the preceding
field nor the following field; the field functions treat it as belonging
to an empty field whose beginning and end are both at pos.
In all of these functions, if pos is omitted or nil, the
value of point is used by default.
- Function: field-beginning &optional pos escape-from-edge
-
This function returns the beginning of the field specified by pos.
If pos is at the beginning of its field, and
escape-from-edge is non-nil, then the return value is
always the beginning of the preceding field that ends at pos,
regardless of the stickiness of the field properties around
pos.
- Function: field-end &optional pos escape-from-edge
-
This function returns the end of the field specified by pos.
If pos is at the end of its field, and escape-from-edge is
non-nil, then the return value is always the end of the following
field that begins at pos, regardless of the stickiness of
the field properties around pos.
- Function: field-string &optional pos
-
This function returns the contents of the field specified by pos,
as a string.
- Function: field-string-no-properties &optional pos
-
This function returns the contents of the field specified by pos,
as a string, discarding text properties.
- Function: delete-field &optional pos
-
This function deletes the text of the field specified by pos.
- Function: constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property
-
This function "constrains" new-pos to the field that
old-pos belongs to--in other words, it returns the position
closest to new-pos that is in the same field as old-pos.
If new-pos is nil, then constrain-to-field uses
the value of point instead, and moves point to the resulting position.
If old-pos is at the boundary of two fields, then the acceptable
positions for new-pos depend on the value of the optional argument
escape-from-edge. If escape-from-edge is nil, then
new-pos is constrained to the field that has the same field
property (either a text-property or an overlay property) that new
characters inserted at old-pos would get. (This depends on the
stickiness of the field property for the characters before and
after old-pos.) If escape-from-edge is non-nil,
new-pos is constrained to the union of the two adjacent fields.
Additionally, if two fields are separated by another field with the
special value boundary, then any point within this special field
is also considered to be "on the boundary."
If the optional argument only-in-line is non-nil, and
constraining new-pos in the usual way would move it to a different
line, new-pos is returned unconstrained. This used in commands
that move by line, such as next-line and
beginning-of-line, so that they respect field boundaries only in
the case where they can still move to the right line.
If the optional argument inhibit-capture-property is
non-nil, and old-pos has a non-nil property of that
name, then any field boundaries are ignored.
You can cause constrain-to-field to ignore all field boundaries
(and so never constrain anything) by binding the variable
inhibit-field-text-motion to a non-nil value.
32.19.11 Why Text Properties are not Intervals
Some editors that support adding attributes to text in the buffer do
so by letting the user specify "intervals" within the text, and adding
the properties to the intervals. Those editors permit the user or the
programmer to determine where individual intervals start and end. We
deliberately provided a different sort of interface in Emacs Lisp to
avoid certain paradoxical behavior associated with text modification.
If the actual subdivision into intervals is meaningful, that means you
can distinguish between a buffer that is just one interval with a
certain property, and a buffer containing the same text subdivided into
two intervals, both of which have that property.
Suppose you take the buffer with just one interval and kill part of
the text. The text remaining in the buffer is one interval, and the
copy in the kill ring (and the undo list) becomes a separate interval.
Then if you yank back the killed text, you get two intervals with the
same properties. Thus, editing does not preserve the distinction
between one interval and two.
Suppose we "fix" this problem by coalescing the two intervals when
the text is inserted. That works fine if the buffer originally was a
single interval. But suppose instead that we have two adjacent
intervals with the same properties, and we kill the text of one interval
and yank it back. The same interval-coalescence feature that rescues
the other case causes trouble in this one: after yanking, we have just
one interval. One again, editing does not preserve the distinction
between one interval and two.
Insertion of text at the border between intervals also raises
questions that have no satisfactory answer.
However, it is easy to arrange for editing to behave consistently for
questions of the form, "What are the properties of this character?"
So we have decided these are the only questions that make sense; we have
not implemented asking questions about where intervals start or end.
In practice, you can usually use the text property search functions in
place of explicit interval boundaries. You can think of them as finding
the boundaries of intervals, assuming that intervals are always
coalesced whenever possible. See section 32.19.3 Text Property Search Functions.
Emacs also provides explicit intervals as a presentation feature; see
38.9 Overlays.
32.20 Substituting for a Character Code
The following functions replace characters within a specified region
based on their character codes.
- Function: subst-char-in-region start end old-char new-char &optional noundo
-
This function replaces all occurrences of the character old-char
with the character new-char in the region of the current buffer
defined by start and end.
If noundo is non-nil, then subst-char-in-region does
not record the change for undo and does not mark the buffer as modified.
This was useful for controlling the old selective display feature
(see section 38.6 Selective Display).
subst-char-in-region does not move point and returns
nil.
| | ---------- Buffer: foo ----------
This is the contents of the buffer before.
---------- Buffer: foo ----------
(subst-char-in-region 1 20 ?i ?X)
=> nil
---------- Buffer: foo ----------
ThXs Xs the contents of the buffer before.
---------- Buffer: foo ----------
|
- Function: translate-region start end table
- This function applies a translation table to the characters in the
buffer between positions start and end.
The translation table table is a string; (aref table
ochar) gives the translated character corresponding to
ochar. If the length of table is less than 256, any
characters with codes larger than the length of table are not
altered by the translation.
The return value of translate-region is the number of
characters that were actually changed by the translation. This does
not count characters that were mapped into themselves in the
translation table.
32.21 Registers
A register is a sort of variable used in Emacs editing that can hold a
variety of different kinds of values. Each register is named by a
single character. All ASCII characters and their meta variants
(but with the exception of C-g) can be used to name registers.
Thus, there are 255 possible registers. A register is designated in
Emacs Lisp by the character that is its name.
- Variable: register-alist
- This variable is an alist of elements of the form
(name .
contents). Normally, there is one element for each Emacs
register that has been used.
The object name is a character (an integer) identifying the
register.
The contents of a register can have several possible types:
- a number
- A number stands for itself. If
insert-register finds a number
in the register, it converts the number to decimal.
- a marker
- A marker represents a buffer position to jump to.
- a string
- A string is text saved in the register.
- a rectangle
- A rectangle is represented by a list of strings.
(window-configuration position)
- This represents a window configuration to restore in one frame, and a
position to jump to in the current buffer.
(frame-configuration position)
- This represents a frame configuration to restore, and a position
to jump to in the current buffer.
- (file filename)
- This represents a file to visit; jumping to this value visits file
filename.
- (file-query filename position)
- This represents a file to visit and a position in it; jumping to this
value visits file filename and goes to buffer position
position. Restoring this type of position asks the user for
confirmation first.
The functions in this section return unpredictable values unless
otherwise stated.
- Function: get-register reg
- This function returns the contents of the register
reg, or
nil if it has no contents.
- Function: set-register reg value
- This function sets the contents of register reg to value.
A register can be set to any value, but the other register functions
expect only certain data types. The return value is value.
- Command: view-register reg
- This command displays what is contained in register reg.
- Command: insert-register reg &optional beforep
- This command inserts contents of register reg into the current
buffer.
Normally, this command puts point before the inserted text, and the
mark after it. However, if the optional second argument beforep
is non-nil, it puts the mark before and point after.
You can pass a non-nil second argument beforep to this
function interactively by supplying any prefix argument.
If the register contains a rectangle, then the rectangle is inserted
with its upper left corner at point. This means that text is inserted
in the current line and underneath it on successive lines.
If the register contains something other than saved text (a string) or
a rectangle (a list), currently useless things happen. This may be
changed in the future.
32.22 Transposition of Text
This subroutine is used by the transposition commands.
- Function: transpose-regions start1 end1 start2 end2 &optional leave-markers
- This function exchanges two nonoverlapping portions of the buffer.
Arguments start1 and end1 specify the bounds of one portion
and arguments start2 and end2 specify the bounds of the
other portion.
Normally, transpose-regions relocates markers with the transposed
text; a marker previously positioned within one of the two transposed
portions moves along with that portion, thus remaining between the same
two characters in their new position. However, if leave-markers
is non-nil, transpose-regions does not do this--it leaves
all markers unrelocated.
32.23 Base 64 Encoding
Base 64 code is used in email to encode a sequence of 8-bit bytes as
a longer sequence of ASCII graphic characters. It is defined in
Internet RFC(7)2045. This section describes the functions for
converting to and from this code.
- Function: base64-encode-region beg end &optional no-line-break
-
This function converts the region from beg to end into base
64 code. It returns the length of the encoded text. An error is
signaled if a character in the region is multibyte, i.e. in a
multibyte buffer the region must contain only characters from the
charsets
ascii, eight-bit-control and
eight-bit-graphic.
Normally, this function inserts newline characters into the encoded
text, to avoid overlong lines. However, if the optional argument
no-line-break is non-nil, these newlines are not added, so
the output is just one long line.
- Function: base64-encode-string string &optional no-line-break
-
This function converts the string string into base 64 code. It
returns a string containing the encoded text. As for
base64-encode-region, an error is signaled if a character in the
string is multibyte.
Normally, this function inserts newline characters into the encoded
text, to avoid overlong lines. However, if the optional argument
no-line-break is non-nil, these newlines are not added, so
the result string is just one long line.
- Function: base64-decode-region beg end
-
This function converts the region from beg to end from base
64 code into the corresponding decoded text. It returns the length of
the decoded text.
The decoding functions ignore newline characters in the encoded text.
- Function: base64-decode-string string
-
This function converts the string string from base 64 code into
the corresponding decoded text. It returns a string containing the
decoded text.
The decoding functions ignore newline characters in the encoded text.
32.24 MD5 Checksum
MD5 cryptographic checksums, or message digests, are 128-bit
"fingerprints" of a document or program. They are used to verify
that you have an exact and unaltered copy of the data. The algorithm
to calculate the MD5 message digest is defined in Internet
RFC(8)1321. This section describes the Emacs facilities for computing
message digests.
- Function: md5 object &optional start end coding-system noerror
- This function returns the MD5 message digest of object, which
should be a buffer or a string.
The two optional arguments start and end are character
positions specifying the portion of object to compute the
message digest for. If they are nil or omitted, the digest is
computed for the whole of object.
The function md5 does not compute the message digest directly
from the internal Emacs representation of the text (see section 33.1 Text Representations). Instead, it encodes the text using a coding
system, and computes the message digest from the encoded text. The
optional fourth argument coding-system specifies which coding
system to use for encoding the text. It should be the same coding
system that you used to read the text, or that you used or will use
when saving or sending the text. See section 33.10 Coding Systems, for more
information about coding systems.
If coding-system is nil or omitted, the default depends
on object. If object is a buffer, the default for
coding-system is whatever coding system would be chosen by
default for writing this text into a file. If object is a
string, the user's most preferred coding system (see section `the description of prefer-coding-system' in GNU Emacs Manual) is used.
Normally, md5 signals an error if the text can't be encoded
using the specified or chosen coding system. However, if
noerror is non-nil, it silently uses raw-text
coding instead.
32.25 Change Hooks
These hook variables let you arrange to take notice of all changes in
all buffers (or in a particular buffer, if you make them buffer-local).
See also 32.19.4 Properties with Special Meanings, for how to detect changes to specific
parts of the text.
The functions you use in these hooks should save and restore the match
data if they do anything that uses regular expressions; otherwise, they
will interfere in bizarre ways with the editing operations that call
them.
- Variable: before-change-functions
- This variable holds a list of functions to call before any buffer
modification. Each function gets two arguments, the beginning and end
of the region that is about to change, represented as integers. The
buffer that is about to change is always the current buffer.
- Variable: after-change-functions
- This variable holds a list of functions to call after any buffer
modification. Each function receives three arguments: the beginning and
end of the region just changed, and the length of the text that existed
before the change. All three arguments are integers. The buffer that's
about to change is always the current buffer.
The length of the old text is the difference between the buffer positions
before and after that text as it was before the change. As for the
changed text, its length is simply the difference between the first two
arguments.
- Macro: combine-after-change-calls body...
- The macro executes body normally, but arranges to call the
after-change functions just once for a series of several changes--if
that seems safe.
If a program makes several text changes in the same area of the buffer,
using the macro combine-after-change-calls around that part of
the program can make it run considerably faster when after-change hooks
are in use. When the after-change hooks are ultimately called, the
arguments specify a portion of the buffer including all of the changes
made within the combine-after-change-calls body.
Warning: You must not alter the values of
after-change-functions within
the body of a combine-after-change-calls form.
Note: If the changes you combine occur in widely scattered
parts of the buffer, this will still work, but it is not advisable,
because it may lead to inefficient behavior for some change hook
functions.
The two variables above are temporarily bound to nil during the
time that any of these functions is running. This means that if one of
these functions changes the buffer, that change won't run these
functions. If you do want a hook function to make changes that run
these functions, make it bind these variables back to their usual
values.
One inconvenient result of this protective feature is that you cannot
have a function in after-change-functions or
before-change-functions which changes the value of that variable.
But that's not a real limitation. If you want those functions to change
the list of functions to run, simply add one fixed function to the hook,
and code that function to look in another variable for other functions
to call. Here is an example:
| | (setq my-own-after-change-functions nil)
(defun indirect-after-change-function (beg end len)
(let ((list my-own-after-change-functions))
(while list
(funcall (car list) beg end len)
(setq list (cdr list)))))
(add-hooks 'after-change-functions
'indirect-after-change-function)
|
- Variable: first-change-hook
- This variable is a normal hook that is run whenever a buffer is changed
that was previously in the unmodified state.
- Variable: inhibit-modification-hooks
-
If this variable is non-
nil, all of the change hooks are
disabled; none of them run. This affects all the hook variables
described above in this section, as well as the hooks attached to
certain special text properties (see section 32.19.4 Properties with Special Meanings) and overlay
properties (see section 38.9.1 Overlay Properties).
This variable is available starting in Emacs 21.
This document was generated
on May 2, 2002
using texi2html