@c This is part of the Emacs manual.
-@c Copyright (C) 1985-1987, 1993-1995, 1997, 2001-2011
-@c Free Software Foundation, Inc.
+@c Copyright (C) 1985-1987, 1993-1995, 1997, 2001-2015 Free Software
+@c Foundation, Inc.
@c See file emacs.texi for copying conditions.
-@node Indentation, Text, Major Modes, Top
+@node Indentation
@chapter Indentation
@cindex indentation
@cindex tabs
@cindex columns (indentation)
- This chapter describes the Emacs commands that add, remove, or
-adjust indentation.
-
-@table @kbd
-@item @key{TAB}
-Indent the current line appropriately, in a mode-dependent fashion.
-@item @kbd{C-j}
-Perform @key{RET} followed by @key{TAB} (@code{newline-and-indent}).
-@item M-^
-Merge the previous and the current line (@code{delete-indentation}).
-This would cancel the effect of a preceding @kbd{C-j}.
-@item C-M-o
-Split the current line at point; text on the line after point becomes a
-new line indented to the same column where point is located
-(@code{split-line}).
-@item M-m
-Move (forward or back) to the first nonblank character on the current
-line (@code{back-to-indentation}).
-@item C-M-\
-Indent lines in the region to the same column (@code{indent-region}).
-@item C-x @key{TAB}
-Shift lines in the region rigidly right or left (@code{indent-rigidly}).
-@item M-i
-Indent from point to the next prespecified tab stop column
-(@code{tab-to-tab-stop}).
-@item M-x indent-relative
-Indent from point to under an indentation point in the previous line.
+@cindex whitespace character
+ @dfn{Indentation} refers to inserting or adjusting @dfn{whitespace
+characters} (space and/or tab characters) at the beginning of a line
+of text. This chapter documents indentation commands and options
+which are common to Text mode and related modes, as well as
+programming language modes. @xref{Program Indent}, for additional
+documentation about indenting in programming modes.
+
+@findex indent-for-tab-command
+@kindex TAB @r{(indentation)}
+ The simplest way to perform indentation is the @key{TAB} key. In
+most major modes, this runs the command @code{indent-for-tab-command}.
+(In C and related modes, @key{TAB} runs the command
+@code{c-indent-line-or-region}, which behaves similarly).
+
+@table @key
+@item TAB
+Insert whitespace, or indent the current line, in a mode-appropriate
+way (@code{indent-for-tab-command}). If the region is active, indent
+all the lines within it.
@end table
-@noindent
-The @key{TAB} key runs @code{indent-for-tab-command} in most major
-modes (in C and related modes, @key{TAB} runs a separate command,
-@code{c-indent-line-or-region}, which behaves similarly). The major
-mode determines just what this entails.
-
- In text modes, @key{TAB} inserts some combination of space and tab
-characters to advance point to the next tab stop (@pxref{Tab Stops}).
-If the region is active and spans multiple lines, it advances the
-first character of each of those lines to the next tab stop
-(@pxref{Using Region}). For the purposes of this command, the
-position of the first non-whitespace character on the preceding line
-is treated as an additional tab stop. Thus, you can use @key{TAB} to
-``align'' point with the preceding line.
-
- In programming modes, @key{TAB} adds or removes some combination of
-space and tab characters at the start of the line, in a way that makes
-sense given the text in the preceding lines. If the region is active
-and spans multiple lines, all those lines are indented this way. If
-point was initially within the current line's indentation, it is
-positioned after that indentation; otherwise, it remains at same point
-in the newly-indented text. @xref{Program Indent}.
-
-@vindex tab-width
- Normally, indentation commands insert (or remove) an optimal mix of
-@dfn{tab characters} and spaces to align to the desired column. Tab
-characters (@acronym{ASCII} code 9) are displayed as a stretch of
-empty space extending to the next @dfn{display tab stop}. By default,
-there is one display tab stop every eight columns; the number of
-columns is determined by the variable @code{tab-width}. You can
-insert a single tab character by typing @kbd{C-q @key{TAB}}.
-@xref{Text Display}.
-
-@findex edit-tab-stops
-@findex tab-to-tab-stop
-@kindex M-i
- The command @kbd{M-i} (@code{tab-to-tab-stop}) adjusts the
-whitespace characters around point, inserting just enough whitespace
-to advance point up to the next tab stop. By default, this involves
-deleting the existing whitespace and inserting a single tab character.
+ The exact behavior of @key{TAB} depends on the major mode. In Text
+mode and related major modes, @key{TAB} normally inserts some
+combination of space and tab characters to advance point to the next
+tab stop (@pxref{Tab Stops}). For this purpose, the position of the
+first non-whitespace character on the preceding line is treated as an
+additional tab stop, so you can use @key{TAB} to ``align'' point with
+the preceding line. If the region is active (@pxref{Using Region}),
+@key{TAB} acts specially: it indents each line in the region so that
+its first non-whitespace character is aligned with the preceding line.
+
+ In programming modes, @key{TAB} indents the current line of code in
+a way that makes sense given the code in the preceding lines. If the
+region is active, all the lines in the region are indented this way.
+If point was initially within the current line's indentation, it is
+repositioned to the first non-whitespace character on the line.
- @xref{Just Spaces}, for how to disable use of tabs. However,
-@kbd{C-q @key{TAB}} always inserts a tab, even when tabs are disabled
-for the indentation commands.
-
-@vindex tab-always-indent
- The variable @code{tab-always-indent} tweaks the behavior of the
-@key{TAB} (@code{indent-for-tab-command}) command. The default value,
-@code{t}, gives the behavior described above. If you change the value
-to the symbol @code{complete}, then @key{TAB} first tries to indent
-the current line, and if the line was already indented, it tries to
-complete the text at point (@pxref{Symbol Completion}). If the value
-is @code{nil}, then @key{TAB} indents the current line only if point
-is at the left margin or in the line's indentation; otherwise, it
-inserts a real tab character.
+ If you just want to insert a tab character in the buffer, type
+@kbd{C-q @key{TAB}} (@pxref{Inserting Text}).
@menu
-* Indentation Commands:: Various commands and techniques for indentation.
-* Tab Stops:: You can set arbitrary "tab stops" and then
- indent to the next tab stop when you want to.
-* Just Spaces:: You can request indentation using just spaces.
+* Indentation Commands:: More commands for performing indentation.
+* Tab Stops:: Stop points for indentation in Text modes.
+* Just Spaces:: Using only space characters for indentation.
+* Indent Convenience:: Optional indentation features.
@end menu
-@node Indentation Commands, Tab Stops, Indentation, Indentation
-@section Indentation Commands and Techniques
+@node Indentation Commands
+@section Indentation Commands
+
+Apart from the @key{TAB} (@code{indent-for-tab-command}) command,
+Emacs provides a variety of commands to perform indentation in other
+ways.
+
+@table @kbd
+@item C-M-o
+@kindex C-M-o
+@findex split-line
+Split the current line at point (@code{split-line}). The text on the
+line after point becomes a new line, indented to the same column where
+point is located. This command first moves point forward over any
+spaces and tabs. Afterward, point is positioned before the inserted
+newline.
@kindex M-m
@findex back-to-indentation
- To move over the indentation on a line, do @kbd{M-m}
-(@code{back-to-indentation}). This command, given anywhere on a line,
-positions point at the first nonblank character on the line, if any,
-or else at the end of the line.
-
- To insert an indented line before the current line, do @kbd{C-a C-o
-@key{TAB}}. To make an indented line after the current line, use
-@kbd{C-e C-j}.
+@item M-m
+Move (forward or back) to the first non-whitespace character on the
+current line (@code{back-to-indentation}). If there are no
+non-whitespace characters on the line, move to the end of the line.
- If you just want to insert a tab character in the buffer, type
-@kbd{C-q @key{TAB}}.
+@item M-i
+@kindex M-i
+@findex tab-to-tab-stop
+Indent whitespace at point, up to the next tab stop
+(@code{tab-to-tab-stop}). @xref{Tab Stops}.
-@kindex C-M-o
-@findex split-line
- @kbd{C-M-o} (@code{split-line}) moves the text from point to the end of
-the line vertically down, so that the current line becomes two lines.
-@kbd{C-M-o} first moves point forward over any spaces and tabs. Then it
-inserts after point a newline and enough indentation to reach the same
-column point is on. Point remains before the inserted newline; in this
-regard, @kbd{C-M-o} resembles @kbd{C-o}.
+@findex indent-relative
+@item M-x indent-relative
+Insert whitespace at point, until point is aligned with the first
+non-whitespace character on the previous line (actually, the last
+non-blank line). If point is already farther right than that, run
+@code{tab-to-tab-stop} instead---unless called with a numeric
+argument, in which case do nothing.
+@item M-^
@kindex M-^
@findex delete-indentation
- To join two lines cleanly, use the @kbd{M-^}
-(@code{delete-indentation}) command. It deletes the indentation at
-the front of the current line, and the line boundary as well,
-replacing them with a single space. As a special case (useful for
-Lisp code) the single space is omitted if the characters to be joined
-are consecutive open parentheses or closing parentheses, or if the
-junction follows another newline. To delete just the indentation of a
-line, go to the beginning of the line and use @kbd{M-\}
-(@code{delete-horizontal-space}), which deletes all spaces and tabs
-around the cursor.
-
- If you have a fill prefix, @kbd{M-^} deletes the fill prefix if it
+Merge the previous and the current line (@code{delete-indentation}).
+This ``joins'' the two lines cleanly, by replacing any indentation at
+the front of the current line, together with the line boundary, with a
+single space.
+
+As a special case (useful for Lisp code), the single space is omitted
+if the characters to be joined are consecutive opening and closing
+parentheses, or if the junction follows another newline.
+
+If there is a fill prefix, @kbd{M-^} deletes the fill prefix if it
appears after the newline that is deleted. @xref{Fill Prefix}.
+@item C-M-\
@kindex C-M-\
-@kindex C-x TAB
@findex indent-region
-@findex indent-rigidly
- There are also commands for changing the indentation of several lines
-at once. They apply to all the lines that begin in the region.
-@kbd{C-M-\} (@code{indent-region}) indents each line in the ``usual''
-way, as if you had typed @key{TAB} at the beginning of the line. A
-numeric argument specifies the column to indent to, and each line is
-shifted left or right so that its first nonblank character appears in
-that column. @kbd{C-x @key{TAB}} (@code{indent-rigidly}) moves all of
-the lines in the region right by its argument (left, for negative
-arguments). The whole group of lines moves rigidly sideways, which is
-how the command gets its name.
+Indent all the lines in the region, as though you had typed @key{TAB}
+at the beginning of each line (@code{indent-region}).
+If a numeric argument is supplied, indent every line in the region to
+that column number.
+
+@item C-x @key{TAB}
+@kindex C-x TAB
+@findex indent-rigidly
@cindex remove indentation
- To remove all indentation from all of the lines in the region,
-invoke @kbd{C-x @key{TAB}} with a large negative argument, such as
--1000.
+This command is used to change the indentation of all lines that begin
+in the region, moving the affected lines as a ``rigid'' unit.
+
+If called with no argument, the command activates a transient mode for
+adjusting the indentation of the affected lines interactively. While
+this transient mode is active, typing @key{LEFT} or @key{RIGHT}
+indents leftward and rightward, respectively, by one space. You can
+also type @kbd{S-@key{LEFT}} or @kbd{S-@key{RIGHT}} to indent leftward
+or rightward to the next tab stop (@pxref{Tab Stops}). Typing any
+other key disables the transient mode, and resumes normal editing.
+
+If called with a prefix argument @var{n}, this command indents the
+lines forward by @var{n} spaces (without enabling the transient mode).
+Negative values of @var{n} indent backward, so you can remove all
+indentation from the lines in the region using a large negative
+argument, like this:
+
+@smallexample
+C-u -999 C-x @key{TAB}
+@end smallexample
+@end table
-@findex indent-relative
- @kbd{M-x indent-relative} indents at point based on the previous line
-(actually, the last nonempty line). It inserts whitespace at point, moving
-point, until it is underneath the next indentation point in the previous line.
-An indentation point is the end of a sequence of whitespace or the end of
-the line. If point is farther right than any indentation point in the
-previous line, @code{indent-relative} runs @code{tab-to-tab-stop}
-@ifnottex
-(@pxref{Tab Stops}),
-@end ifnottex
-@iftex
-(see next section),
-@end iftex
-unless it is called with a numeric argument, in which case it does
-nothing.
-
- @xref{Format Indentation}, for another way of specifying the
-indentation for part of your text.
-
-@node Tab Stops, Just Spaces, Indentation Commands, Indentation
+@node Tab Stops
@section Tab Stops
-
@cindex tab stops
-@cindex using tab stops in making tables
-@cindex tables, indentation for
-@kindex M-i
-@findex tab-to-tab-stop
- For typing in tables, you can use @kbd{M-i} (@code{tab-to-tab-stop}).
-This command inserts indentation before point, enough to reach the
-next tab stop column.
+
+@vindex tab-stop-list
+ Emacs defines certain column numbers to be @dfn{tab stops}. These
+are used as stopping points by @key{TAB} when inserting whitespace in
+Text mode and related modes (@pxref{Indentation}), and by commands
+like @kbd{M-i} (@pxref{Indentation Commands}). The variable
+@code{tab-stop-list} controls these positions. The default value is
+@code{nil}, which means a tab stop every 8 columns. The value can
+also be a list of zero-based column numbers (in increasing order) at
+which to place tab stops. Emacs extends the list forever by repeating
+the difference between the last and next-to-last elements.
@findex edit-tab-stops
-@findex edit-tab-stops-note-changes
@kindex C-c C-c @r{(Edit Tab Stops)}
-@vindex tab-stop-list
- You can change the tab stops used by @kbd{M-i} and other indentation
-commands, so that they need not be spaced every eight characters, or
-even regularly spaced. The tab stops are stored in the variable
-@code{tab-stop-list}, as a list of column numbers in increasing order.
-
- A convenient way to set the tab stops is with @kbd{M-x
-edit-tab-stops}, which creates and selects a buffer containing a
-description of the tab stop settings. You can edit this buffer to
-specify different tab stops, and then type @kbd{C-c C-c} to make those
-new tab stops take effect. The buffer uses Overwrite mode
-(@pxref{Minor Modes}). @code{edit-tab-stops} records which buffer was
-current when you invoked it, and stores the tab stops back in that
-buffer; normally all buffers share the same tab stops and changing
-them in one buffer affects all, but if you happen to make
-@code{tab-stop-list} local in one buffer then @code{edit-tab-stops} in
-that buffer will edit the local settings.
-
- Here is what the text representing the tab stops looks like for ordinary
-tab stops every eight columns.
+ Instead of customizing the variable @code{tab-stop-list} directly, a
+convenient way to view and set tab stops is via the command @kbd{M-x
+edit-tab-stops}. This switches to a buffer containing a description
+of the tab stop settings, which looks like this:
@example
: : : : : :
To install changes, type C-c C-c
@end example
- The first line contains a colon at each tab stop. The remaining lines
-are present just to help you see where the colons are and know what to do.
+@noindent
+The first line contains a colon at each tab stop. The numbers on the
+next two lines are present just to indicate where the colons are.
+If the value of @code{tab-stop-list} is @code{nil}, as it is by default,
+no colons are displayed initially.
+
+ You can edit this buffer to specify different tab stops by placing
+colons on the desired columns. The buffer uses Overwrite mode
+(@pxref{Minor Modes}). Remember that Emacs will extend the list of
+tab stops forever by repeating the difference between the last two
+explicit stops that you place. When you are done, type @kbd{C-c C-c} to make
+the new tab stops take effect. Normally, the new tab stop settings
+apply to all buffers. However, if you have made the
+@code{tab-stop-list} variable local to the buffer where you called
+@kbd{M-x edit-tab-stops} (@pxref{Locals}), then the new tab stop
+settings apply only to that buffer. To save the tab stop settings for
+future Emacs sessions, use the Customize interface to save the value
+of @code{tab-stop-list} (@pxref{Easy Customization}).
+
+ Note that the tab stops discussed in this section have nothing to do
+with how tab characters are displayed in the buffer. Tab characters
+are always displayed as empty spaces extending to the next
+@dfn{display tab stop}. @xref{Text Display}.
+
+@node Just Spaces
+@section Tabs vs. Spaces
- Note that the tab stops that control @code{tab-to-tab-stop} have
-nothing to do with how tab characters are displayed in the buffer.
-Tab characters are always displayed as empty spaces extending to the
-next display tab stop, which occurs every @code{tab-width} columns
-regardless of the contents of @code{tab-stop-list}. @xref{Text
+@vindex tab-width
+ Normally, indentation commands insert (or remove) an optimal mix of
+space characters and tab characters to align to the desired column.
+Tab characters are displayed as a stretch of empty space extending to
+the next @dfn{display tab stop}. By default, there is one display tab
+stop every @code{tab-width} columns (the default is 8). @xref{Text
Display}.
-@node Just Spaces,, Tab Stops, Indentation
-@section Tabs vs. Spaces
-
@vindex indent-tabs-mode
- Emacs normally uses both tabs and spaces to indent lines. If you
-prefer, all indentation can be made from spaces only. To request
-this, set @code{indent-tabs-mode} to @code{nil}. This is a per-buffer
-variable, so altering the variable affects only the current buffer,
-but there is a default value which you can change as well.
-@xref{Locals}.
-
- A tab is not always displayed in the same way. By default, tabs are
-eight columns wide, but some people like to customize their editors to
-use a different tab width (e.g., by changing the variable
-@code{tab-width} in Emacs). By using spaces only, you can make sure
-that your file looks the same regardless of the tab width setting.
+ If you prefer, all indentation can be made from spaces only. To
+request this, set the buffer-local variable @code{indent-tabs-mode} to
+@code{nil}. @xref{Locals}, for information about setting buffer-local
+variables. Note, however, that @kbd{C-q @key{TAB}} always inserts a
+tab character, regardless of the value of @code{indent-tabs-mode}.
+
+ One reason to set @code{indent-tabs-mode} to @code{nil} is that not
+all editors display tab characters in the same way. Emacs users, too,
+may have different customized values of @code{tab-width}. By using
+spaces only, you can make sure that your file always looks the same.
+If you only care about how it looks within Emacs, another way to
+tackle this problem is to set the @code{tab-width} variable in a
+file-local variable (@pxref{File Variables}).
@findex tabify
@findex untabify
There are also commands to convert tabs to spaces or vice versa, always
-preserving the columns of all nonblank text. @kbd{M-x tabify} scans the
+preserving the columns of all non-whitespace text. @kbd{M-x tabify} scans the
region for sequences of spaces, and converts sequences of at least two
spaces to tabs if that can be done without changing indentation. @kbd{M-x
untabify} changes all tabs in the region to appropriate numbers of spaces.
+
+@node Indent Convenience
+@section Convenience Features for Indentation
+
+@vindex tab-always-indent
+ The variable @code{tab-always-indent} tweaks the behavior of the
+@key{TAB} (@code{indent-for-tab-command}) command. The default value,
+@code{t}, gives the behavior described in @ref{Indentation}. If you
+change the value to the symbol @code{complete}, then @key{TAB} first
+tries to indent the current line, and if the line was already
+indented, it tries to complete the text at point (@pxref{Symbol
+Completion}). If the value is @code{nil}, then @key{TAB} indents the
+current line only if point is at the left margin or in the line's
+indentation; otherwise, it inserts a tab character.
+
+@cindex Electric Indent mode
+@cindex mode, Electric Indent
+@findex electric-indent-mode
+ Electric Indent mode is a global minor mode that automatically
+indents the line after every @key{RET} you type. This mode is enabled
+by default. To toggle this minor mode, type @kbd{M-x
+electric-indent-mode}. To toggle the mode in a single buffer,
+use @kbd{M-x electric-indent-local-mode}.