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1
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2 @node Indentation, Text, Major Modes, Top
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3 @chapter Indentation
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4 @cindex indentation
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5
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6 @c WideCommands
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7 @table @kbd
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8 @item @key{TAB}
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9 Indent current line ``appropriately'' in a mode-dependent fashion.
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10 @item @key{LFD}
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11 Perform @key{RET} followed by @key{TAB} (@code{newline-and-indent}).
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12 @item M-^
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13 Merge two lines (@code{delete-indentation}). This would cancel out
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14 the effect of @key{LFD}.
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15 @item C-M-o
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16 Split line at point; text on the line after point becomes a new line
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17 indented to the same column that it now starts in (@code{split-line}).
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18 @item M-m
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19 Move (forward or back) to the first non-blank character on the current
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20 line (@code{back-to-indentation}).
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21 @item C-M-\
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22 Indent several lines to same column (@code{indent-region}).
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23 @item C-x @key{TAB}
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24 Shift block of lines rigidly right or left (@code{indent-rigidly}).
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25 @item M-i
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26 Indent from point to the next prespecified tab stop column
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27 (@code{tab-to-tab-stop}).
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28 @item M-x indent-relative
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29 Indent from point to under an indentation point in the previous line.
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30 @end table
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31
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32 @kindex TAB
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33 @cindex indentation
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34 Most programming languages have some indentation convention. For Lisp
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35 code, lines are indented according to their nesting in parentheses. The
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36 same general idea is used for C code, though details differ.
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37
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38 Use the @key{TAB} command to indent a line whatever the language.
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39 Each major mode defines this command to perform indentation appropriate
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40 for the particular language. In Lisp mode, @key{TAB} aligns a line
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41 according to its depth in parentheses. No matter where in the line you
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42 are when you type @key{TAB}, it aligns the line as a whole. In C mode,
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43 @key{TAB} implements a subtle and sophisticated indentation style that
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44 knows about many aspects of C syntax.
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45
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46 @kindex TAB
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47 In Text mode, @key{TAB} runs the command @code{tab-to-tab-stop}, which
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48 indents to the next tab stop column. You can set the tab stops with
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49 @kbd{M-x edit-tab-stops}.
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50
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51 @menu
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52 * Indentation Commands:: Various commands and techniques for indentation.
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53 * Tab Stops:: You can set arbitrary "tab stops" and then
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54 indent to the next tab stop when you want to.
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55 * Just Spaces:: You can request indentation using just spaces.
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56 @end menu
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57
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58 @node Indentation Commands, Tab Stops, Indentation, Indentation
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59 @section Indentation Commands and Techniques
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60 @c ??? Explain what Emacs has instead of space-indent-flag.
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61
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62 If you just want to insert a tab character in the buffer, you can type
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63 @kbd{C-q @key{TAB}}.
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64
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65 @kindex M-m
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66 @findex back-to-indentation
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67 To move over the indentation on a line, type @kbd{Meta-m}
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68 (@code{back-to-indentation}). This command, given anywhere on a line,
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69 positions point at the first non-blank character on the line.
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70
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71 To insert an indented line before the current line, type @kbd{C-a C-o
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72 @key{TAB}}. To make an indented line after the current line, use
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73 @kbd{C-e @key{LFD}}.
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74
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75 @kindex C-M-o
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76 @findex split-line
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77 @kbd{C-M-o} (@code{split-line}) moves the text from point to the end of
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78 the line vertically down, so that the current line becomes two lines.
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79 @kbd{C-M-o} first moves point forward over any spaces and tabs. Then it
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80 inserts after point a newline and enough indentation to reach the same
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81 column point is on. Point remains before the inserted newline; in this
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82 regard, @kbd{C-M-o} resembles @kbd{C-o}.
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83
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84 @kindex M-\
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85 @kindex M-^
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86 @findex delete-horizontal-space
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87 @findex delete-indentation
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88 To join two lines cleanly, use the @kbd{Meta-^}
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89 (@code{delete-indentation}) command to delete the indentation at the
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90 front of the current line, and the line boundary as well. Empty spaces
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91 are replaced by a single space, or by no space if at the beginning of a
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92 line, before a close parenthesis, or after an open parenthesis.
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93 To delete just the indentation of a line, go to the beginning of the
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94 line and use @kbd{Meta-\} (@code{delete-horizontal-space}), which
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95 deletes all spaces and tabs around the cursor.
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96
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97 @kindex C-M-\
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98 @kindex C-x TAB
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99 @findex indent-region
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100 @findex indent-rigidly
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101 There are also commands for changing the indentation of several lines at
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102 once. @kbd{Control-Meta-\} (@code{indent-region}) gives each line which
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103 begins in the region the ``usual'' indentation by invoking @key{TAB} at the
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104 beginning of the line. A numeric argument specifies the column to indent
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105 to. Each line is shifted left or right so that its first non-blank
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106 character appears in that column. @kbd{C-x @key{TAB}}
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107 (@code{indent-rigidly}) moves all the lines in the region right by its
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108 argument (left, for negative arguments). The whole group of lines moves
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109 rigidly sideways, which is how the command gets its name.@refill
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110
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111 @findex indent-relative
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112 @kbd{M-x indent-relative} indents at point based on the previous line
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113 (actually, the last non-empty line.) It inserts whitespace at point, moving
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114 point, until it is underneath an indentation point in the previous line.
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115 An indentation point is the end of a sequence of whitespace or the end of
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116 the line. If point is farther right than any indentation point in the
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117 previous line, the whitespace before point is deleted and the first
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118 indentation point then applicable is used. If no indentation point is
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119 applicable even then, @code{tab-to-tab-stop} is run (see next section).
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120
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121 @code{indent-relative} is the definition of @key{TAB} in Indented Text
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122 mode. @xref{Text}.
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123
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124 @node Tab Stops, Just Spaces, Indentation Commands, Indentation
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125 @section Tab Stops
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126
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127 @kindex M-i
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128 @findex tab-to-tab-stop
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129 For typing in tables, you can use Text mode's definition of @key{TAB},
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130 @code{tab-to-tab-stop}. This command inserts indentation before point,
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131 enough to reach the next tab stop column. Even if you are not in Text mode,
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132 this function is associated with @kbd{M-i} anyway.
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133
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134 @findex edit-tab-stops
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135 @findex edit-tab-stops-note-changes
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136 @kindex C-c C-c (Edit Tab Stops)
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137 @vindex tab-stop-list
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138 You can arbitrarily set the tab stops used by @kbd{M-i}. They are
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139 stored as a list of column-numbers in increasing order in the variable
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140 @code{tab-stop-list}.
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141
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142 The convenient way to set the tab stops is using @kbd{M-x edit-tab-stops},
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143 which creates and selects a buffer containing a description of the tab stop
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144 settings. You can edit this buffer to specify different tab stops, and
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145 then type @kbd{C-c C-c} to make those new tab stops take effect. In the
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146 tab stop buffer, @kbd{C-c C-c} runs the function
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147 @code{edit-tab-stops-note-changes} rather than the default
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148 @code{save-buffer}. @code{edit-tab-stops} records which buffer was current
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149 when you invoked it, and stores the tab stops in that buffer. Normally
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150 all buffers share the same tab stops and changing them in one buffer
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151 affects all. If you make @code{tab-stop-list} local in one
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152 buffer @code{edit-tab-stops} in that buffer edits only the local
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153 settings.
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154
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155 Below is the text representing ordinary tab stops every eight columns:
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156
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157 @example
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158 : : : : : :
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159 0 1 2 3 4
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160 0123456789012345678901234567890123456789012345678
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161 To install changes, type C-c C-c
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162 @end example
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163
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164 The first line contains a colon at each tab stop. The remaining lines
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165 help you see where the colons are and tell you what to do.
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166
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167 Note that the tab stops that control @code{tab-to-tab-stop} have nothing
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168 to do with displaying tab characters in the buffer. @xref{Display Vars},
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169 for more information on that.
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170
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171 @node Just Spaces,, Tab Stops, Indentation
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172 @section Tabs vs. Spaces
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173
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174 @vindex indent-tabs-mode
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175 Emacs normally uses both tabs and spaces to indent lines. If you prefer,
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176 all indentation can be made from spaces only. To request this, set
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177 @code{indent-tabs-mode} to @code{nil}. This is a per-buffer variable;
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178 altering the variable affects only the current buffer, but there is a
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179 default value which you can change as well. @xref{Locals}.
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180
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181 @findex tabify
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182 @findex untabify
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183 There are also commands to convert tabs to spaces or vice versa, always
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184 preserving the columns of all non-blank text. @kbd{M-x tabify} scans the
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185 region for sequences of spaces, and converts sequences of at least three
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186 spaces to tabs if that is possible without changing indentation. @kbd{M-x
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187 untabify} changes all tabs in the region to corresponding numbers of spaces.
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