264 lines
11 KiB
Text
264 lines
11 KiB
Text
@c This is part of the Emacs manual.
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@c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2001, 2002,
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@c 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
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@c See file emacs.texi for copying conditions.
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@node Indentation, Text, Major Modes, Top
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@chapter Indentation
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@cindex indentation
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@cindex tabs
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@cindex columns (indentation)
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This chapter describes the Emacs commands that add, remove, or
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adjust indentation.
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@table @kbd
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@item @key{TAB}
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Indent the current line appropriately, in a mode-dependent fashion.
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@item @kbd{C-j}
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Perform @key{RET} followed by @key{TAB} (@code{newline-and-indent}).
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@item M-^
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Merge the previous and the current line (@code{delete-indentation}).
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This would cancel the effect of a preceding @kbd{C-j}.
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@item C-M-o
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Split the current line at point; text on the line after point becomes a
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new line indented to the same column where point is located
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(@code{split-line}).
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@item M-m
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Move (forward or back) to the first nonblank character on the current
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line (@code{back-to-indentation}).
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@item C-M-\
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Indent lines in the region to the same column (@code{indent-region}).
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@item C-x @key{TAB}
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Shift lines in the region rigidly right or left (@code{indent-rigidly}).
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@item M-i
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Indent from point to the next prespecified tab stop column
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(@code{tab-to-tab-stop}).
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@item M-x indent-relative
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Indent from point to under an indentation point in the previous line.
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@end table
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@noindent
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The @key{TAB} key runs @code{indent-for-tab-command} in most major
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modes (in C and related modes, @key{TAB} runs a separate command,
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@code{c-indent-line-or-region}, which behaves similarly). The major
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mode determines just what this entails.
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In text modes, @key{TAB} inserts some combination of space and tab
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characters to advance point to the next tab stop (@pxref{Tab Stops}).
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If the region is active and spans multiple lines, it advances the
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first character of each of those lines to the next tab stop
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(@pxref{Using Region}). For the purposes of this command, the
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position of the first non-whitespace character on the preceding line
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is treated as an additional tab stop. Thus, you can use @key{TAB} to
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``align'' point with the preceding line.
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In programming modes, @key{TAB} adds or removes some combination of
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space and tab characters at the start of the line, in a way that makes
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sense given the text in the preceding lines. If the region is active
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and spans multiple lines, all those lines are indented this way. If
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point was initially within the current line's indentation, it is
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positioned after that indentation; otherwise, it remains at same point
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in the newly-indented text. @xref{Program Indent}.
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@vindex tab-width
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Normally, indentation commands insert (or remove) an optimal mix of
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@dfn{tab characters} and spaces to align to the desired column. Tab
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characters (@acronym{ASCII} code 9) are displayed as a stretch of
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empty space extending to the next @dfn{display tab stop}. By default,
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there is one display tab stop every eight columns; the number of
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columns is determined by the variable @code{tab-width}. You can
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insert a single tab character by typing @kbd{C-q @key{TAB}}.
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@xref{Text Display}.
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@findex edit-tab-stops
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@findex tab-to-tab-stop
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@kindex M-i
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The command @kbd{M-i} (@code{tab-to-tab-stop}) adjusts the
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whitespace characters around point, inserting just enough whitespace
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to advance point up to the next tab stop. By default, this involves
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deleting the existing whitespace and inserting a single tab character.
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@xref{Just Spaces}, for how to disable use of tabs. However,
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@kbd{C-q @key{TAB}} always inserts a tab, even when tabs are disabled
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for the indentation commands.
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@vindex tab-always-indent
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The variable @code{tab-always-indent} tweaks the behavior of the
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@key{TAB} (@code{indent-for-tab-command}) command. The default value,
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@code{t}, gives the behavior described above. If you change the value
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to the symbol @code{complete}, then @key{TAB} first tries to indent
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the current line, and if the line was already indented, it tries to
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complete the text at point (@pxref{Symbol Completion}). If the value
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is @code{nil}, then @key{TAB} indents the current line only if point
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is at the left margin or in the line's indentation; otherwise, it
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inserts a real tab character.
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@menu
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* Indentation Commands:: Various commands and techniques for indentation.
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* Tab Stops:: You can set arbitrary "tab stops" and then
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indent to the next tab stop when you want to.
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* Just Spaces:: You can request indentation using just spaces.
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@end menu
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@node Indentation Commands, Tab Stops, Indentation, Indentation
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@section Indentation Commands and Techniques
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@kindex M-m
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@findex back-to-indentation
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To move over the indentation on a line, do @kbd{M-m}
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(@code{back-to-indentation}). This command, given anywhere on a line,
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positions point at the first nonblank character on the line, if any,
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or else at the end of the line.
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To insert an indented line before the current line, do @kbd{C-a C-o
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@key{TAB}}. To make an indented line after the current line, use
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@kbd{C-e C-j}.
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If you just want to insert a tab character in the buffer, type
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@kbd{C-q @key{TAB}}.
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@kindex C-M-o
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@findex split-line
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@kbd{C-M-o} (@code{split-line}) moves the text from point to the end of
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the line vertically down, so that the current line becomes two lines.
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@kbd{C-M-o} first moves point forward over any spaces and tabs. Then it
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inserts after point a newline and enough indentation to reach the same
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column point is on. Point remains before the inserted newline; in this
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regard, @kbd{C-M-o} resembles @kbd{C-o}.
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@kindex M-^
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@findex delete-indentation
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To join two lines cleanly, use the @kbd{M-^}
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(@code{delete-indentation}) command. It deletes the indentation at
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the front of the current line, and the line boundary as well,
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replacing them with a single space. As a special case (useful for
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Lisp code) the single space is omitted if the characters to be joined
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are consecutive open parentheses or closing parentheses, or if the
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junction follows another newline. To delete just the indentation of a
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line, go to the beginning of the line and use @kbd{M-\}
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(@code{delete-horizontal-space}), which deletes all spaces and tabs
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around the cursor.
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If you have a fill prefix, @kbd{M-^} deletes the fill prefix if it
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appears after the newline that is deleted. @xref{Fill Prefix}.
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@kindex C-M-\
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@kindex C-x TAB
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@findex indent-region
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@findex indent-rigidly
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There are also commands for changing the indentation of several lines
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at once. They apply to all the lines that begin in the region.
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@kbd{C-M-\} (@code{indent-region}) indents each line in the ``usual''
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way, as if you had typed @key{TAB} at the beginning of the line. A
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numeric argument specifies the column to indent to, and each line is
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shifted left or right so that its first nonblank character appears in
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that column. @kbd{C-x @key{TAB}} (@code{indent-rigidly}) moves all of
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the lines in the region right by its argument (left, for negative
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arguments). The whole group of lines moves rigidly sideways, which is
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how the command gets its name.
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@cindex remove indentation
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To remove all indentation from all of the lines in the region,
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invoke @kbd{C-x @key{TAB}} with a large negative argument, such as
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-1000.
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@findex indent-relative
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@kbd{M-x indent-relative} indents at point based on the previous line
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(actually, the last nonempty line). It inserts whitespace at point, moving
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point, until it is underneath the next indentation point in the previous line.
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An indentation point is the end of a sequence of whitespace or the end of
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the line. If point is farther right than any indentation point in the
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previous line, @code{indent-relative} runs @code{tab-to-tab-stop}
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@ifnottex
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(@pxref{Tab Stops}),
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@end ifnottex
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@iftex
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(see next section),
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@end iftex
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unless it is called with a numeric argument, in which case it does
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nothing.
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@xref{Format Indentation}, for another way of specifying the
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indentation for part of your text.
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@node Tab Stops, Just Spaces, Indentation Commands, Indentation
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@section Tab Stops
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@cindex tab stops
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@cindex using tab stops in making tables
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@cindex tables, indentation for
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@kindex M-i
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@findex tab-to-tab-stop
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For typing in tables, you can use @kbd{M-i} (@code{tab-to-tab-stop}).
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This command inserts indentation before point, enough to reach the
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next tab stop column.
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@findex edit-tab-stops
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@findex edit-tab-stops-note-changes
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@kindex C-c C-c @r{(Edit Tab Stops)}
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@vindex tab-stop-list
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You can change the tab stops used by @kbd{M-i} and other indentation
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commands, so that they need not be spaced every eight characters, or
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even regularly spaced. The tab stops are stored in the variable
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@code{tab-stop-list}, as a list of column numbers in increasing order.
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A convenient way to set the tab stops is with @kbd{M-x
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edit-tab-stops}, which creates and selects a buffer containing a
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description of the tab stop settings. You can edit this buffer to
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specify different tab stops, and then type @kbd{C-c C-c} to make those
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new tab stops take effect. The buffer uses Overwrite mode
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(@pxref{Minor Modes}). @code{edit-tab-stops} records which buffer was
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current when you invoked it, and stores the tab stops back in that
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buffer; normally all buffers share the same tab stops and changing
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them in one buffer affects all, but if you happen to make
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@code{tab-stop-list} local in one buffer then @code{edit-tab-stops} in
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that buffer will edit the local settings.
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Here is what the text representing the tab stops looks like for ordinary
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tab stops every eight columns.
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@example
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: : : : : :
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0 1 2 3 4
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0123456789012345678901234567890123456789012345678
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To install changes, type C-c C-c
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@end example
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The first line contains a colon at each tab stop. The remaining lines
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are present just to help you see where the colons are and know what to do.
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Note that the tab stops that control @code{tab-to-tab-stop} have
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nothing to do with how tab characters are displayed in the buffer.
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Tab characters are always displayed as empty spaces extending to the
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next display tab stop, which occurs every @code{tab-width} columns
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regardless of the contents of @code{tab-stop-list}. @xref{Text
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Display}.
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@node Just Spaces,, Tab Stops, Indentation
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@section Tabs vs. Spaces
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@vindex indent-tabs-mode
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Emacs normally uses both tabs and spaces to indent lines. If you
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prefer, all indentation can be made from spaces only. To request
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this, set @code{indent-tabs-mode} to @code{nil}. This is a per-buffer
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variable, so altering the variable affects only the current buffer,
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but there is a default value which you can change as well.
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@xref{Locals}.
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A tab is not always displayed in the same way. By default, tabs are
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eight columns wide, but some people like to customize their editors to
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use a different tab width (e.g., by changing the variable
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@code{tab-width} in Emacs). By using spaces only, you can make sure
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that your file looks the same regardless of the tab width setting.
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@findex tabify
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@findex untabify
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There are also commands to convert tabs to spaces or vice versa, always
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preserving the columns of all nonblank text. @kbd{M-x tabify} scans the
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region for sequences of spaces, and converts sequences of at least two
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spaces to tabs if that can be done without changing indentation. @kbd{M-x
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untabify} changes all tabs in the region to appropriate numbers of spaces.
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@ignore
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arch-tag: acc07de7-ae11-4ee8-a159-cb59c473f0fb
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@end ignore
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