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1 \input texinfo @c -*-texinfo-*-
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2 @setfilename ../info/R2L
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3 @settitle Right-to-left writing
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4
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5 @titlepage
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6 @sp 6
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7 @center @titlefont{Right-to-left writing}
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8 @sp 4
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9 @center Version 2.0
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10 @sp 5
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11 @center Ken'ichi HANDA
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12 @center handa@@etl.go.jp
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13 @page
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14
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15 @end titlepage
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16
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17 @comment ============================================================
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18 @node Top, , , (mule)
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19 @section Right-to-left writing
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20
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21 This document describes how Mule handles a text written from right to
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22 left.
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23
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24 @menu
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25 * Right-to-left Character Set::
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26 * Direction of Buffer::
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27 * Cursor Motion::
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28 * LR Commands::
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29 @ignore
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30 * Double cursor::
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31 * Highlighing::
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32 * Visual inputting::
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33 @end ignore
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34 @end menu
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35
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36 @comment ============================================================
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37 @node Right-to-left Character Set, Direction of Buffer, , Top
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38 @section Right-to-left Character Set
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39
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40 In Mule, each character set has the attribute @dfn{direction}. The
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41 value is either 0 (l2r, left-to-right) or 1 (r2l, right-to-left). For
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42 the moment, Mule has four r2l character sets, namely, Hebrew
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43 (ISO8859-8), ASCII-r2l (private) Arabic1 (private) and Arabic2
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44 (private). ASCII-r2l is for providing r2l space and punctuation
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45 characters to Hebrew. Consecutive r2l characters are shown from right
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46 to left on the screen.
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47
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48 Hereafter, we denote r2l characters by capital letters and l2r
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49 characters by lowercase letters in strings. Punctuation marks (e.g.,
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50 period) mean normal ASCII characters. For r2l space and punctuations,
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51 we use the letter @samp{_} (underscore).
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52
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53 @comment ============================================================
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54 @node Direction of Buffer, Cursor Motion, Right-to-left character set, Top
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55 @section Direction of buffer
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56
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57 Each buffer also has the attribute @dfn{direction} (buffer local
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58 variable @code{display-direction}). By default, the value is @code{nil}
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59 (means l2r direction). Provided that a buffer contains:
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60
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61 @example
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62 this is a DESREVER word.
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63 @end example
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64
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65 If @code{display-direction} is @code{nil} (this is the default), what
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66 you see on your screen is:
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67
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68 @example
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69 +---------------------------------+
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70 |this is a DESREVER word. |
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71 | |
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72 +---------------------------------+
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73 @end example
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74
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75 but, if the direction is non-@code{nil}, what you see is:
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76
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77 @example
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78 +---------------------------------+
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79 | word.DESREVERthis is a |
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80 | |
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81 +---------------------------------+
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82 @end example
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83
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84 If you are in visual-mode, the value of @code{display-direction} is
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85 reflected in the mode-line. The string @samp{L2R} means
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86 @code{display-direction} is @code{nil}; @samp{R2L} means non-@code{nil}.
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87 In visual-mode, you can set @code{display-direction} to @code{nil} by
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88 typing @kbd{C-c <}, and to @code{t} (this means non-@code{nil}) by
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89 typing @kbd{C-c >}.
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90
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91 If you read a file that has the extension @file{.l2r}, the buffer
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92 automatically turns into visual-mode and @code{display-direction} is set
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93 to @code{nil}. Likewise, if a file has the extension @file{.r2l}, the
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94 buffer automatically goes in visual-mode and @code{display-direction} is
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95 set to @code{t}.
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96
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97 @comment ============================================================
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98 @node Cursor Motion, LR commands, Direction of Buffer, Top
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99 @section Cursor Motion
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100
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101 If you are not in visual-mode and type @kbd{C-f} (or @kbd{M-x
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102 forward-char}, the cursor moves as follows:
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103
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104 @example
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105 |this is a DESREVER word. |
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106 ^
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107 |this is a DESREVER word. |
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108 ^
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109 |this is a DESREVER word. |
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110 ^
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111 |this is a DESREVER word. |
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112 ^
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113 |this is a DESREVER word. |
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114 ^
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115 |this is a DESREVER word. |
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116 ^
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117 |this is a DESREVER word. |
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118 ^
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119 |this is a DESREVER word. |
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120 ^
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121 |this is a DESREVER word. |
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122 ^
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123 |this is a DESREVER word. |
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124 ^
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125 |this is a DESREVER word. |
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126 ^
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127 |this is a DESREVER word. |
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128 ^
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129 |this is a DESREVER word. |
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130 ^
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131 |this is a DESREVER word. |
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132 ^
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133 @end example
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134
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135 This is rather complicated and misleading. To avoid confusions, the
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136 following cursor motion commands are prepared in visual-mode to handle
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137 bi-directional texts easily. All these commands accept an additional
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138 prefix numeric argument.
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139
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140 @table @asis
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141 @item @kbd{C-f} or @kbd{M-x visual-forward-char}
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142 Move the cursor visually forward in characters.
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143
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144 @item @kbd{C-b} or @kbd{M-x visual-backward-char}
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145 Move the cursor visually backward in characters.
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146
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147 @item @kbd{C-p}, @kbd{@key{UP}} or @kbd{M-x visual-previous-line}
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148 Move the cursor up in lines.
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149
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150 @item @kbd{C-n}, @kbd{@key{DOWN}} or @kbd{M-x visual-next-line}
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151 Move the cursor down in lines.
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152
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153 @item @kbd{C-a} or @kbd{M-x visual-beginning-of-line}
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154 Move the cursor to the visual beginning of the current line.
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155
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156 @item @kbd{M-f} or @kbd{M-x visual-forward-word}
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157 Move the cursor visually forward in words.
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158
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159 @item @kbd{M-b} or @kbd{M-x visual-backward-word}
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160 Move the cursor visually backward in words.
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161
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162 @item @kbd{M-<}, @kbd{HOME} or @kbd{M-x visual-beginning-of-buffer}
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163 Move the cursor to the visual beginning of the current buffer.
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164
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165 @item @kbd{M->}, @kbd{END} or @kbd{M-x visual-end-of-buffer}
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166 Move the cursor to the visual end of the current buffer.
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167 @end table
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168
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169 Note that ordinary cursor motion commands (@code{forward-char},
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170 @code{backward-char}, etc.) behave according to the @dfn{logical order}
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171 of the text, whilst the above commands behave according to the
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172 @dfn{visual order}. Compare the difference of the two @kbd{C-f}
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173 commands. (You can exit visual-mode by typing @kbd{C-c C-c}.)
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174
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175 Some of you may be confused by the words @dfn{forward} and
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176 @dfn{backward}. Here is a summary:
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177
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178 @example
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179 display-direction nil non-nil
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180 ------------------------------------------------
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181 forward right left
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182 backward left right
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183 @end example
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184
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185 @comment ============================================================
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186 @node LR Commands, , Cursor Motion, Top
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187 @section LR Commands
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188
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189 If you have been using Emacs or Mule for a long time, it is possible
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190 that @kbd{C-b} and @dfn{move to left} are so strongly associated in your
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191 mind that you want to move the cursor to left by @kbd{C-b} no matter how
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192 @code{display-direction} is set. Likewise, you may want to move the
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193 cursor to the right, to the left-most column and to the right-most
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194 column by @kbd{C-f}, @kbd{C-a} and @kbd{C-e}, respectively.
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195
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196 In such cases, include the following line in your @file{~/.emacs}
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197 file:
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198
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199 @lisp
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200 (setq visual-use-lr-commands t)
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201 @end lisp
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202
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203 This lisp command enables so called @dfn{LR commands}. LR commands
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204 act according to the absolute screen direction (such as @dfn{left} or
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205 @dfn{right}) rather than the relative direction (@dfn{forward} or
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206 @dfn{backward}).
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207
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208 @table @asis
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209 @item @kbd{C-b}, @kbd{@key{LEFT}} or @kbd{M-x visual-move-to-left-char}
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210 Move the cursor to the left in characters.
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211
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212 @item @kbd{C-f}, @kbd{@key{RIGHT}} or @kbd{M-x visual-move-to-right-char}
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213 Move the cursor to the right in characters.
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214
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215 @item @kbd{M-b}, @kbd{@key{M-LEFT}} or @kbd{M-x visual-move-to-left-word}
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216 Move the cursor to the left in words.
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217
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218 @item @kbd{M-f}, @kbd{@key{M-RIGHT}} or @kbd{M-x visual-move-to-right-word}
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219 Move the cursor to the right in words.
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220
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221 @item @kbd{C-a} or @kbd{M-x visual-left-end-of-line}
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222 Move the cursor to the left-most column of the current line.
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223
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224 @item @kbd{C-e} or @kbd{M-x visual-right-end-of-line}
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225 Move the cursor to the right-most column of the current line.
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226 @end table
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227
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228 As a matter of fact, the four keys, @key{LEFT}, @key{RIGHT},
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229 @key{M-LEFT} and @key{M-RIGHT} are active even though your
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230 @file{~/.emacs} file does not contain the @code{setq} line above. So if
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231 you are confused, use the arrow keys.
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232
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233 @ignore
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234
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235 @node Double cursor, Highlighing, Direction of buffer, Top
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236 @section Double cursor
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237
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238 If the value of 'r2l-double-cursor' is non-nil, when POINT
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239 is in between r2l char and l2r (normal) char, two cursor are
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240 displayed to denote insertion points for both types of
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241 character. For instance, in the above example, when you
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242 move POINT forward one by one, the cursor changes as
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243 follows:
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244
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245 @example
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246 |this is a WERBEH word. |
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247 ^
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248 |this is a WERBEH word. |
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249 ^
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250 |this is a WERBEH word. |
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251 ^ ^
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252 |this is a WERBEH word. |
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253 ^
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254 |this is a WERBEH word. |
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255 ^
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256 |this is a WERBEH word. |
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257 ^
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258 |this is a WERBEH word. |
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259 ^
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260 |this is a WERBEH word. |
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261 ^
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262 |this is a WERBEH word. |
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263 ^ ^
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264 |this is a WERBEH word. |
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265 ^
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266 @end example
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267
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268 @node Highlighing, Visual inputting, Double cursor, Top
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269 @section Highlighing characters of reverse direction
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270
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271 If the value of 'highlight-reverse-direction' is non-nil
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272 (default), a character whose direction is different from
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273 that of the current buffer is highlighted by gray-color (or
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274 background mesh).
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275
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276 @node Visual inputting, , Highlighing, Top
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277 @section Visual inputting
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278
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279 As mentioned above, cursor motion in r2l text is rather complicated.
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280 Further, even with the double cursor function, you may need some time
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281 to learn inserting/deleting characters in an r2l text.
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282
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283 To faciliate the manipulation of r2l texts, quail provides a set of
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284 functions which make cursor motion and insertion/deletion behave as
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285 you expect.
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286
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287 visually-forward-char
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288 Function: Move cursor visually forward by ARG chars.
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289
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290 visually-backward-char
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291 Function: Move cursor visually backward by ARG chars.
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292
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293 visually-beginning-of-line
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294 Function: Move cursor to the visually beginning of line.
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295
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296 visually-insert-char
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297 Function: With argument CH, call VISUALLY-INSERT-CHAR ARG times.
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298
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299 visually-backward-delete-char
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300 Function: Delete ARG chars visually before cursor.
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301
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302 visually-delete-char
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303 Function: Delete ARG chars under cursor.
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304
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305 These functions behave as if the whole buffer were filled with
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306 characters of same direction: for example, when the buffer direction
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307 is l2r, visually-forward-char moves the cursor to the right (or left,
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308 if the buffer direction is r2l) step by step; visually-insert-char
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309 puts the typed character just under the cursor and moves the cursor to
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310 the right (left) by one column; visually-backward-delete-char removes
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311 the character left (right) to the cursor, etc.
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312
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313 In quail/hebrew.el these visual functions are called via appropriate
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314 quail cursor motion functions. As quail cursor motion functions are
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315 bound to appropriate keys, you will not be puzzled by the complicated
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316 cursor behaviours as long as you use the hebrew package of quail-mode.
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317
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318 @end ignore
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319
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320 @contents
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321 @bye
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