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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 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 Markers) or numeric
character positions (see section 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 | Examining text in the vicinity of point. | |
32.2 Examining Buffer Contents | Examining text in a general fashion. | |
32.3 Comparing Text | Comparing substrings of buffers. | |
32.4 Inserting Text | Adding new text to a buffer. | |
32.5 User-Level Insertion Commands | User-level commands to insert text. | |
32.6 Deleting Text | Removing text from a buffer. | |
32.7 User-Level Deletion Commands | User-level commands to delete text. | |
32.8 The Kill Ring | Where removed text sometimes is saved for later use. | |
32.9 Undo | Undoing changes to the text of a buffer. | |
32.10 Maintaining Undo Lists | How to enable and disable undo information. How to control how much information is kept. | |
32.11 Filling | Functions for explicit filling. | |
32.12 Margins for Filling | How to specify margins for filling commands. | |
32.13 Adaptive Fill Mode | Adaptive Fill mode chooses a fill prefix from context. | |
32.14 Auto Filling | How auto-fill mode is implemented to break lines. | |
32.15 Sorting Text | Functions for sorting parts of the buffer. | |
32.16 Counting Columns | Computing horizontal positions, and using them. | |
32.17 Indentation | Functions to insert or adjust indentation. | |
32.18 Case Changes | Case conversion of parts of the buffer. | |
32.19 Text Properties | Assigning Lisp property lists to text characters. | |
32.20 Substituting for a Character Code | Replacing a given character wherever it appears. | |
32.22 Transposition of Text | Swapping two portions of a buffer. | |
32.21 Registers | How registers are implemented. Accessing the text or position stored in a register. | |
32.23 Base 64 Encoding | Conversion to or from base 64 encoding. | |
32.24 MD5 Checksum | Compute the MD5 “message digest”/“checksum”. | |
32.25 Change Hooks | Supplying functions to be run when text is changed. |
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Many functions are provided to look at the characters around point.
Several simple functions are described here. See also looking-at
in Regular Expression Searching.
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)) ⇒ "@" |
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.
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" |
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.
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
Point.
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 Point.
This function returns t
if point is at the beginning of a line.
See section Motion by Text Lines. The beginning of the buffer (or of its accessible
portion) always counts as the beginning of a line.
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.
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This section describes two functions that allow a Lisp program to convert any portion of the text in the buffer into a string.
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 Text Properties. However, overlays (see section 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 " |
This is like buffer-substring
, except that it does not copy text
properties, just the characters themselves. See section Text Properties.
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 " |
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 |
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This function lets you compare portions of the text in a buffer, without copying them into strings first.
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 |
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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 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 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 Converting Text Representations.
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
.
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.
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 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 Stickiness of Text Properties.
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 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.
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This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs.
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
.
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 Auto Filling).
This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (See section Abbrevs and Abbrev Expansion, and Table of Syntax Classes.)
This is also responsible for calling blink-paren-function
when
the inserted character has close parenthesis syntax (see section 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.
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 Margins for Filling.
The value returned is nil
. In an interactive call, count
is the numeric prefix argument.
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.
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).
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Deletion means removing part of the text in a buffer, without saving it in the kill ring (see section The Kill Ring). Deleted text can’t be yanked, but can be reinserted using the undo mechanism (see section 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
.
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.
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.
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.
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
.
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
.
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
.
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.
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This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs.
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 ----------
|
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 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.
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 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 ---------- |
This command replaces any spaces and tabs around point with a single
space. It returns nil
.
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
.
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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 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 | What text looks like in the kill ring. | |
32.8.2 Functions for Killing | Functions that kill text. | |
32.8.3 Functions for Yanking | Commands that access the kill ring. | |
32.8.4 Low-Level Kill Ring | Functions and variables for kill ring access. | |
32.8.5 Internals of the Kill Ring | Variables that hold kill-ring data. |
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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.
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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.
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.
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.
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 Low-Level Kill Ring.
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Yanking means reinserting an entry of previously killed text from the kill ring. The text properties are copied too.
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
.
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
.
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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 Window System Selections).
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.
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).
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).
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 Window System Selections.
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 Window System Selections.
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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
).
This variable holds the list of killed text sequences, most recently killed first.
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.
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.
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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
.
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.
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.
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.
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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.
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.
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
.
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.
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.
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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 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 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.
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 (emacs)Paragraphs section ‘Paragraphs’ in The GNU Emacs Manual.
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 Standard Regular Expressions Used in Editing.
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.
This variable alters the action of fill-individual-paragraphs
as
described above.
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 Adaptive Fill Mode.
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.
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
.
This function returns the proper justification style to use for filling the text around point.
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.
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)) |
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.
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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.
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 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.
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.
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.
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.
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
.
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.
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.
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.
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.
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.
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.
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Adaptive Fill mode chooses a fill prefix automatically from the text in each paragraph being filled.
Adaptive Fill mode is enabled when this variable is non-nil
.
It is t
by default.
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.
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.
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.
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.
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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 Filling.
Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. See section Margins for Filling.
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 toauto-fill-function
in version 19.
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.
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.
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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 Functions that Rearrange Lists).
The values returned by these functions are not meaningful.
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
.
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.
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.
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.
If this variable is non-nil
, sort-subr
and the other
buffer sorting functions ignore case when comparing strings.
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 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:
then the text matched by the digitth ‘\(...\)’ parenthesis grouping in record-regexp is the sort key.
then the whole record is the sort key.
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 ‘^.*$’ and set key-regexp to ‘\<f\w*\>’. The resulting expression looks like this:
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>" (region-beginning) (region-end)) |
If you call sort-regexp-fields
interactively, it prompts for
record-regexp and key-regexp in the minibuffer.
This command alphabetically sorts lines in the region between
start and end. If reverse is non-nil
, the sort
is in reverse order.
This command alphabetically sorts paragraphs in the region between
start and end. If reverse is non-nil
, the sort
is in reverse order.
This command alphabetically sorts pages in the region between
start and end. If reverse is non-nil
, the sort
is in reverse order.
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.
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.
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.
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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 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.
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 Motion by Text Lines.
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.
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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 | Functions used to count and insert indentation. | |
32.17.2 Indentation Controlled by Major Mode | Customize indentation for different modes. | |
32.17.3 Indenting an Entire Region | Indent all the lines in a region. | |
32.17.4 Indentation Relative to Previous Lines | Indent the current line based on previous lines. | |
32.17.5 Adjustable “Tab Stops” | Adjustable, typewriter-like tab stops. | |
32.17.6 Indentation-Based Motion Commands | Move to first non-blank character. |
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This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. See section Width, for related functions.
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.
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 Stickiness of Text Properties.
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.
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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.
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).
This command calls the function in indent-line-function
to
indent the current line in a way appropriate for the current major mode.
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.)
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
.
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
.
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This section describes commands that indent all the lines in the region. They return unpredictable values.
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.
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.
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.
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
).
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This section describes two commands that indent the current line based on the contents of previous lines.
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. |
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.
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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 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.
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.
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.
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These commands, primarily for interactive use, act based on the indentation in the text.
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
.
This command moves point backward arg lines and then to the
first nonblank character on that line. It returns nil
.
This command moves point forward arg lines and then to the first
nonblank character on that line. It returns nil
.
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The case change commands described here work on text in the current buffer. See section Case Conversion in Lisp, for case conversion functions that work on strings and characters. See section The Case Table, for how to customize which characters are upper or lower case and how to convert them.
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 ---------- |
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.
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.
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.
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.
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.
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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 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 | Looking at the properties of one character. | |
32.19.2 Changing Text Properties | Setting the properties of a range of text. | |
32.19.3 Text Property Search Functions | Searching for where a property changes value. | |
32.19.4 Properties with Special Meanings | Particular properties with special meanings. | |
32.19.5 Formatted Text Properties | Properties for representing formatting of text. | |
32.19.6 Stickiness of Text Properties | How inserted text gets properties from neighboring text. | |
32.19.7 Saving Text Properties in Files | Saving text properties in files, and reading them back. | |
32.19.8 Lazy Computation of Text Properties | Computing text properties in a lazy fashion only when text is examined. | |
32.19.9 Defining Clickable Text | Using text properties to make regions of text do something when you click on them. | |
32.19.10 Defining and Using Fields | The field property defines
fields within the buffer.
| |
32.19.11 Why Text Properties are not Intervals | Why text properties do not use Lisp-visible text intervals. |
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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 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.
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.
This function is like get-text-property
, except that it checks
overlays first and then text properties. See section 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.
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.
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 |
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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 Undo).
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.
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 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)) |
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 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.
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
:
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 Examining Buffer Contents) which copies text from the buffer
but does not copy its properties.
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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.
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)))
|
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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 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;
(foreground-color . color-name)
or
(background-color . color-name)
. These elements specify
just the foreground color or just the background color.
(foreground-color . color-name)
is equivalent to
(:foreground color-name)
, and likewise for the background.
See section 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 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 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:
help-echo
text property was found.
help-echo
property, and pos is the position in the overlay’s buffer under
the mouse.
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 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 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 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 Read-Only Buffers.
invisible
A non-nil
invisible
property can make a character invisible
on the screen. See section 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 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 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:
point-left
property of the character after the old location,
and
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.
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
.
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 Simple Menu Items,
see section Extended Menu Items), or tool bar help strings (see section Tool bars). The specified function is called with one argument, the help
string to display. Tooltip mode (see (emacs)Tooltips section ‘Tooltips’ in The GNU Emacs Manual) provides an example.
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These text properties affect the behavior of the fill commands. They are used for representing formatted text. See section Filling, and 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.
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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.
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:
Insert the strings strings, just like the function insert
,
but inherit any sticky properties from the adjoining text.
Insert the strings strings, just like the function
insert-before-markers
, but inherit any sticky properties from the
adjoining text.
See section Inserting Text, for the ordinary insertion functions which do not inherit.
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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:
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 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.
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 File Format Conversion, for a related feature.
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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
.
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
.
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.
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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.
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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 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.
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.
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.
This function returns the contents of the field specified by pos, as a string.
This function returns the contents of the field specified by pos, as a string, discarding text properties.
This function deletes the text of the field specified by pos.
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.
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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 Text Property Search Functions.
Emacs also provides explicit intervals as a presentation feature; see Overlays.
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The following functions replace characters within a specified region based on their character codes.
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 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 ---------- |
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.
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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.
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 stands for itself. If insert-register
finds a number
in the register, it converts the number to decimal.
A marker represents a buffer position to jump to.
A string is text saved in the register.
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.
This represents a file to visit; jumping to this value visits file filename.
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.
This function returns the contents of the register
reg, or nil
if it has no contents.
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.
This command displays what is contained in register reg.
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.
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This subroutine is used by the transposition commands.
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.
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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.
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.
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.
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.
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.
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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.
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 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 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 prefer-coding-system: (emacs)Recognize Coding 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.
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