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1
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2 @node Keystrokes, Pull-down Menus, Frame, Top
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3 @chapter Keystrokes, Key Sequences, and Key Bindings
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4
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5 @iftex
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6 This chapter discusses the character set Emacs uses for input commands
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7 and inside files. You have already learned that the more frequently
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8 used Emacs commands are bound to keys. For example, @kbd{Control-f} is
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9 bound to @code{forward-char}. The following issues are covered:
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10
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11 @itemize @bullet
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12 @item
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13 How keystrokes can be represented
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14 @item
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15 How you can create key sequences from keystrokes
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16 @item
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17 How you can add to the available modifier keys by customizing your
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18 keyboard: for example, you could have the
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19 @key{Capslock} key be understood as the @key{Super} key by Emacs. A
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20 @key{Super} key is used like @key{Control} or @key{Meta} in that you hold
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21 it while typing another key.
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22 @end itemize
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23
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24 You will also learn how to customize existing key bindings and
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25 create new ones.
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26 @end iftex
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27
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28 @menu
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29 * Intro to Keystrokes:: Keystrokes as building blocks of key sequences.
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30 * Representing Keystrokes:: Using lists of modifiers and keysyms to
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31 represent keystrokes.
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32 * Key Sequences:: Combine key strokes into key sequences you can
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33 bind to commands.
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34 * String Key Sequences:: Available for upward compatibility.
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35 * Meta Key:: Using @key{ESC} to represent @key{Meta}
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36 * Super and Hyper Keys:: Adding modifier keys on certain keyboards.
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37 * Character Representation:: How characters appear in Emacs buffers.
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38 * Commands:: How commands are bound to key sequences.
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39 @end menu
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40
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41 @node Intro to Keystrokes, Representing Keystrokes, Keystrokes, Keystrokes
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42 @section Keystrokes as Building Blocks of Key Sequences
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43 @cindex character set
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44 @cindex ASCII
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45 @cindex keystroke
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46
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47 Earlier versions of Emacs used only the ASCII character set,
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48 which defines 128 different character codes. Some of these codes are
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49 assigned graphic symbols like @samp{a} and @samp{=}; the rest are
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50 control characters, such as @kbd{Control-a} (also called @kbd{C-a}).
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51 @kbd{C-a} means you hold down the @key{CTRL} key and then press
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52 @kbd{a}.@refill
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53
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54 Keybindings in XEmacs are not restricted to the set of
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55 keystrokes that can be represented in ASCII. XEmacs can tell the
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56 difference between, for example, @kbd{Control-h}, @kbd{Control-Shift-h},
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57 and @kbd{Backspace}.
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58
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59 @cindex modifier key
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60 @cindex keysym
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61 @kindex meta key
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62 @kindex control key
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63 @kindex hyper key
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64 @kindex super key
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65 @kindex shift key
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66 @kindex button1
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67 @kindex button2
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68 @kindex button3
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69 @kindex button1up
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70 @kindex button2up
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71 @kindex button3up
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72
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73 A keystroke is like a piano chord: you get it by simultaneously
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74 striking several keys. To be more precise, a keystroke consists
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75 of a possibly empty set of modifiers followed by a single
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76 @dfn{keysym}. The set of modifiers is small; it consists of
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77 @kbd{Control}, @kbd{Meta}, @kbd{Super}, @kbd{Hyper}, and @kbd{Shift}.
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78
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79 The rest of the keys on your keyboard, along with the mouse buttons,
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80 make up the set of keysyms. A keysym is usually what is printed on the
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81 keys on your keyboard. Here is a table of some of the symbolic names
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82 for keysyms:
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83 @table @kbd
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84 @item a,b,c...
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85 alphabetic keys
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86 @item f1,f2...
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87 function keys
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88 @item button1
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89 left mouse button
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90 @item button2
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91 middle mouse button
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92 @item button3
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93 right mouse button
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94 @item button1up
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95 upstroke on the left mouse button
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96 @item button2up
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97 upstroke on the middle mouse button
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98 @item button3up
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99 upstroke on the right mouse button
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100 @item return
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101 Return key
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102 @end table
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103
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104 @vindex keyboard-translate-table
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105 Use the variable @code{keyboard-translate-table} only if you are on a
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106 dumb tty, as it cannot handle input that cannot be represented as ASCII.
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107 The value of this variable is a string used as a translate table for
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108 keyboard input or @code{nil}. Each character is looked up in this
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109 string and the contents used instead. If the string is of length
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110 @code{n}, character codes @code{N} and up are untranslated. If you are
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111 running Emacs under X, you should do the translations with the
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112 @code{xmodmap} program instead.
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113
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114
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115 @node Representing Keystrokes, Key Sequences, Intro to Keystrokes, Keystrokes
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116 @comment node-name, next, previous, up
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117 @subsection Representing Keystrokes
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118 @kindex hyper key
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119 @kindex super key
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120 @findex read-key-sequence
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121
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122 XEmacs represents keystrokes as lists. Each list consists of
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123 an arbitrary combination of modifiers followed by a single keysym at the
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124 end of the list. If the keysym corresponds to an ASCII character, you
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125 can use its character code. (A keystroke may also be represented by an
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126 event object, as returned by the @code{read-key-sequence} function;
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127 non-programmers need not worry about this.)
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128
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129 The following table gives some examples of how to list representations
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130 for keystrokes. Each list consists of sets of modifiers followed by
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131 keysyms:
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132
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133 @table @kbd
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134 @item (control a)
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135 Pressing @key{CTRL} and @kbd{a} simultaneously.
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136 @item (control ?a)
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137 Another way of writing the keystroke @kbd{C-a}.
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138 @item (control 65)
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139 Yet another way of writing the keystroke @kbd{C-a}.
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140 @item (break)
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141 Pressing the @key{BREAK} key.
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142 @item (control meta button2up)
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143 Release the middle mouse button, while pressing @key{CTRL} and
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144 @key{META}.
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145 @end table
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442
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146 @cindex shift modifier
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428
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147 Note: As you define keystrokes, you can use the @kbd{shift} key only
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148 as a modifier with characters that do not have a second keysym on the
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149 same key, such as @kbd{backspace} and @kbd{tab}. It is an error to
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150 define a keystroke using the @key{shift} modifier with keysyms such as
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151 @kbd{a} and @kbd{=}. The correct forms are @kbd{A} and @kbd{+}.
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152
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153 @node Key Sequences, String Key Sequences, Representing Keystrokes, Keystrokes
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154 @subsection Representing Key Sequences
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155
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156 A @dfn{complete key sequence} is a sequence of keystrokes that Emacs
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157 understands as a unit. Key sequences are significant because you can
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158 bind them to commands. Note that not all sequences of keystrokes are
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159 possible key sequences. In particular, the initial keystrokes in a key
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160 sequence must make up a @dfn{prefix key sequence}.
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161
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162 Emacs represents a key sequence as a vector of keystrokes. Thus, the
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163 schematic representation of a complete key sequence is as follows:
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164
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165 @example
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442
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166 [(modifier .. modifier keysym) ... (modifier .. modifier keysym)]
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428
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167 @end example
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168
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169 Here are some examples of complete key sequences:
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170
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171 @table @kbd
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440
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172 @item [(control c) (control a)]
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428
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173 Typing @kbd{C-c} followed by @kbd{C-a}
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440
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174 @item [(control c) (control 65)]
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428
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175 Typing @kbd{C-c} followed by @kbd{C-a}. (Using the ASCII code
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176 for the character `a')@refill
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177 @item [(control c) (break)]
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178 Typing @kbd{C-c} followed by the @kbd{break} character.@refill
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179 @end table
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180
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181 @kindex C-c
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182 @kindex C-x
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183 @kindex C-h
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184 @kindex ESC
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185 @cindex prefix key sequence
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186
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187 A @dfn{prefix key sequence} is the beginning of a series of longer
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188 sequences that are valid key sequences; adding any single keystroke to
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189 the end of a prefix results in a valid key sequence. For example,
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190 @kbd{control-x} is standardly defined as a prefix. Thus there is a
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191 two-character key sequence starting with @kbd{C-x} for each valid
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192 keystroke, giving numerous possibilities. Here are some samples:
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193
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194 @itemize @bullet
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195 @item
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196 @kbd{[(control x) (c)]}
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197 @item
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198 @kbd{[(control x) (control c)]}
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199 @end itemize
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200
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201 Adding one character to a prefix key does not have to form a complete
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202 key. It could make another, longer prefix. For example, @kbd{[(control
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203 x) (\4)]} is itself a prefix that leads to any number of different
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204 three-character keys, including @kbd{[(control x) (\4) (f)]},
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205 @kbd{[(control x) (\4) (b)]} and so on. It would be possible to define
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206 one of those three-character sequences as a prefix, creating a series of
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207 four-character keys, but we did not define any of them this way.@refill
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208
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209 By contrast, the two-character sequence @kbd{[(control f) (control
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210 k)]} is not a key, because the @kbd{(control f)} is a complete key
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211 sequence in itself. You cannot give @kbd{[(control f (control k)]} an
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212 independent meaning as a command while @kbd{(control f)} is a complete
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213 sequence, because Emacs would understand @key{C-f C-k} as two
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214 commands.@refill
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215
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216 The predefined prefix key sequences in Emacs are @kbd{(control c)},
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217 @kbd{(control x)}, @kbd{(control h)}, @kbd{[(control x) (\4)]}, and
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218 @kbd{escape}. You can customize Emacs and could make new prefix keys or
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219 eliminate the default key sequences. @xref{Key Bindings}. For example,
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220 if you redefine @kbd{(control f)} as a prefix, @kbd{[(control f)
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221 (control k)]} automatically becomes a valid key sequence (complete,
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222 unless you define it as a prefix as well). Conversely, if you remove
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223 the prefix definition of @kbd{[(control x) (\4)]}, @kbd{[(control x)
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224 (\4) (f)]} (or @kbd{[(control x) (\4) @var{anything}]}) is no longer a
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225 valid key sequence.
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226
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227 Note that the above paragraphs uses \4 instead of simply 4, because \4
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228 is the symbol whose name is "4", and plain 4 is the integer 4, which
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229 would have been interpreted as the ASCII value. Another way of
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230 representing the symbol whose name is "4" is to write ?4, which would be
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231 interpreted as the number 52, which is the ASCII code for the character
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232 "4". We could therefore actually have written 52 directly, but that is
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233 far less clear.
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234
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235 @node String Key Sequences, Meta Key, Key Sequences, Keystrokes
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236 @comment node-name, next, previous, up
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237 @subsection String Key Sequences
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238 For backward compatibility, you may also represent a key sequence using
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239 strings. For example, we have the following equivalent representations:
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240
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241 @table @kbd
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242 @item "\C-c\C-c"
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243 @code{[(control c) (control c)]}
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244 @item "\e\C-c"
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245 @code{[(meta control c)]}
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246 @end table
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247
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248 @kindex LFD
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249 @kindex TAB
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250
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251 @node Meta Key, Super and Hyper Keys, String Key Sequences, Keystrokes
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252 @comment node-name, next, previous, up
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253 @subsection Assignment of the @key{META} Key
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254
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255 @kindex META
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256 @kindex ESC
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257 Not all terminals have the complete set of modifiers.
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258 Terminals that have a @key{Meta} key allow you to type Meta characters
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259 by just holding that key down. To type @kbd{Meta-a}, hold down
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260 @key{META} and press @kbd{a}. On those terminals, the @key{META} key
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261 works like the @key{SHIFT} key. Such a key is not always labeled
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262 @key{META}, however, as this function is often a special option for a
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263 key with some other primary purpose.@refill
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264
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265 If there is no @key{META} key, you can still type Meta characters
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266 using two-character sequences starting with @key{ESC}. To enter
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267 @kbd{M-a}, you could type @kbd{@key{ESC} a}. To enter @kbd{C-M-a}, you
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268 would type @kbd{ESC C-a}. @key{ESC} is allowed on terminals with
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269 Meta keys, too, in case you have formed a habit of using it.@refill
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270
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271 If you are running under X and do not have a @key{META} key, it
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272 is possible to reconfigure some other key to be a @key{META}
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273 key. @xref{Super and Hyper Keys}. @refill
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274
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275 @vindex meta-flag
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276 Emacs believes the terminal has a @key{META} key if the variable
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277 @code{meta-flag} is non-@code{nil}. Normally this is set automatically
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278 according to the termcap entry for your terminal type. However, sometimes
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279 the termcap entry is wrong, and then it is useful to set this variable
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280 yourself. @xref{Variables}, for how to do this.
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281
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282 Note: If you are running under the X window system, the setting of
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283 the @code{meta-flag} variable is irrelevant.
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284
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285 @node Super and Hyper Keys, Character Representation, Meta Key, Keystrokes
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286 @comment node-name, next, previous, up
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287 @subsection Assignment of the @key{SUPER} and @key{HYPER} Keys
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288 @kindex hyper key
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289 @kindex super key
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290
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291 Most keyboards do not, by default, have @key{SUPER} or @key{HYPER}
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292 modifier keys. Under X, you can simulate the @key{SUPER} or
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293 @key{HYPER} key if you want to bind keys to sequences using @kbd{super}
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294 and @kbd{hyper}. You can use the @code{xmodmap} program to do this.
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295
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296 For example, to turn your @key{CAPS-LOCK} key into a @key{SUPER} key,
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297 do the following:
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298
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299 Create a file called @code{~/.xmodmap}. In this file, place the lines
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300
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301 @example
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440
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302 remove Lock = Caps_Lock
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303 keysym Caps_Lock = Super_L
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304 add Mod2 = Super_L
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428
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305 @end example
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306
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307 The first line says that the key that is currently called @code{Caps_Lock}
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308 should no longer behave as a ``lock'' key. The second line says that
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309 this should now be called @code{Super_L} instead. The third line says that
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310 the key called @code{Super_L} should be a modifier key, which produces the
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311 @code{Mod2} modifier.
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312
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313 To create a @key{META} or @key{HYPER} key instead of a @key{SUPER} key,
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314 replace the word @code{Super} above with @code{Meta} or @code{Hyper}.
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315
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316 Just after you start up X, execute the command @code{xmodmap /.xmodmap}.
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317 You can add this command to the appropriate initialization file to have
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318 the command executed automatically.@refill
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319
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320 If you have problems, see the documentation for the @code{xmodmap}
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321 program. The X keyboard model is quite complicated, and explaining
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322 it is beyond the scope of this manual. However, we reprint the
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323 following description from the X Protocol document for your convenience:
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324
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325 @cindex keysyms
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326 @cindex keycode
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327
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328 A list of keysyms is associated with each keycode. If that list
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329 (ignoring trailing @code{NoSymbol} entries) is a single keysym @samp{K},
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330 then the list is treated as if it were the list
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331 @code{``K NoSymbol K NoSymbol''}. If the list (ignoring trailing
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332 @code{NoSymbol} entries) is a pair of keysyms @samp{K1 K2}, then the
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333 list is treated as if it were the list @code{``K1 K2 K1 K2''}. If the
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334 list (ignoring trailing @code{NoSymbol} entries) is a triple of keysyms
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335 @samp{K1 K2 K3}, then the list is treated as if it were the list
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336 @code{``K1 K2 K3 NoSymbol''}.
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337
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338 The first four elements of the list are split into two groups of
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339 keysyms. Group 1 contains the first and second keysyms; Group 2 contains
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340 third and fourth keysyms. Within each group, if the second element of
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341 the group is NoSymbol, then the group should be treated as if the second
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342 element were the same as the first element, except when the first
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343 element is an alphabetic keysym @samp{K} for which both lowercase and
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344 uppercase forms are defined. In that case, the group should be treated
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345 as if the first element were the lowercase form of @samp{K} and the second
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346 element were the uppercase form of @samp{K}.
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347
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348 The standard rules for obtaining a keysym from a KeyPress event make use of
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349 only the Group 1 and Group 2 keysyms; no interpretation of other keysyms in
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350 the list is given here. (That is, the last four keysyms are unused.)
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351
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352 Which group to use is determined by modifier state. Switching between
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353 groups is controlled by the keysym named @code{Mode_switch}. Attach that
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354 keysym to some keycode and attach that keycode to any one of the
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355 modifiers Mod1 through Mod5. This modifier is called the @dfn{group
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356 modifier}. For any keycode, Group 1 is used when the group modifier is
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357 off, and Group 2 is used when the group modifier is on.
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358
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359 Within a group, which keysym to use is also determined by modifier
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360 state. The first keysym is used when the @code{Shift} and @code{Lock}
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361 modifiers are off. The second keysym is used when the @code{Shift}
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362 modifier is on, or when the @code{Lock} modifier is on and the second
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363 keysym is uppercase alphabetic, or when the @code{Lock} modifier is on
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364 and is interpreted as @code{ShiftLock}. Otherwise, when the @code{Lock}
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365 modifier is on and is interpreted as @code{CapsLock}, the state of the
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366 @code{Shift} modifier is applied first to select a keysym,
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367 but if that keysym is lower-case alphabetic, then the corresponding
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368 upper-case keysym is used instead.
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369
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370 In addition to the above information on keysyms, we also provide the
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371 following description of modifier mapping from the InterClient
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372 Communications Conventions Manual:
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373
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374 @cindex modifier mapping
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375
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376 X11 supports 8 modifier bits, of which 3 are pre-assigned to
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377 @code{Shift}, @code{Lock}, and @code{Control}. Each modifier bit is
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378 controlled by the state of a set of keys, and these sets are specified
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379 in a table accessed by @code{GetModifierMapping()} and
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380 @code{SetModifierMapping()}.
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381
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382 A client needing to use one of the pre-assigned modifiers should assume
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383 that the modifier table has been set up correctly to control these
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384 modifiers. The @code{Lock} modifier should be interpreted as @code{Caps
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385 Lock} or @code{Shift Lock} according to whether the keycodes in its
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386 controlling set include @code{XK_Caps_Lock} or @code{XK_Shift_Lock}.
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387
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388 Clients should determine the meaning of a modifier bit from the keysyms
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389 being used to control it.
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390
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391 A client needing to use an extra modifier, for example @code{Meta}, should:
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392
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393 @enumerate
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394 @item
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395 Scan the existing modifier mappings.
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396
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397 @enumerate
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398 @item
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399 If it finds a modifier that contains a keycode whose set of keysyms
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400 includes @code{XK_Meta_L} or @code{XK_Meta_R}, it should use that
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401 modifier bit.
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402
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403 @item
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404 If there is no existing modifier controlled by @code{XK_Meta_L} or
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405 @code{XK_Meta_R}, it should select an unused modifier bit (one with
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406 an empty controlling set) and:
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407 @end enumerate
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408
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409 @item
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410 If there is a keycode with @code{XL_Meta_L} in its set of keysyms,
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411 add that keycode to the set for the chosen modifier, and then:
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412
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413 @enumerate
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414 @item
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415 If there is a keycode with @code{XL_Meta_R} in its set of keysyms,
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416 add that keycode to the set for the chosen modifier, and then:
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417
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418 @item
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419 If the controlling set is still empty, interact with the user to
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420 select one or more keys to be @code{Meta}.
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421 @end enumerate
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422
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423
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424 @item
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425 If there are no unused modifier bits, ask the user to take corrective action.
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426 @end enumerate
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427
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428 This means that the @code{Mod1} modifier does not necessarily mean
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429 @code{Meta}, although some applications (such as twm and emacs 18)
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430 assume that. Any of the five unassigned modifier bits could mean
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431 @code{Meta}; what matters is that a modifier bit is generated by a
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432 keycode which is bound to the keysym @code{Meta_L} or @code{Meta_R}.
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433
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434 Therefore, if you want to make a @key{META} key, the right way
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435 is to make the keycode in question generate both a @code{Meta} keysym
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436 and some previously-unassigned modifier bit.
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437
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438 @node Character Representation, Commands, Super and Hyper Keys, Keystrokes
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439 @comment node-name, next, previous, up
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440 @section Representation of Characters
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441
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442 This section briefly discusses how characters are represented in Emacs
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443 buffers. @xref{Key Sequences}, for information on representing key
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444 sequences to create key bindings.
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445
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446 ASCII graphic characters in Emacs buffers are displayed with their
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447 graphics. @key{LFD} is the same as a newline character; it is displayed
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448 by starting a new line. @key{TAB} is displayed by moving to the next
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449 tab stop column (usually every 8 spaces). Other control characters are
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450 displayed as a caret (@samp{^}) followed by the non-control version of
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451 the character; thus, @kbd{C-a} is displayed as @samp{^A}. Non-ASCII
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452 characters 128 and up are displayed with octal escape sequences; thus,
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453 character code 243 (octal), also called @kbd{M-#} when used as an input
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454 character, is displayed as @samp{\243}.
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455
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456 The variable @code{ctl-arrow} may be used to alter this behavior.
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457 @xref{Display Vars}.
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458
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459 @node Commands, , Character Representation, Keystrokes
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460 @section Keys and Commands
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461
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462 @cindex binding
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463 @cindex customization
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464 @cindex keymap
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465 @cindex function
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466 @cindex command
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467 This manual is full of passages that tell you what particular keys do.
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468 But Emacs does not assign meanings to keys directly. Instead, Emacs
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469 assigns meanings to @dfn{functions}, and then gives keys their meanings
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470 by @dfn{binding} them to functions.
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471
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472 A function is a Lisp object that can be executed as a program. Usually
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473 it is a Lisp symbol that has been given a function definition; every
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474 symbol has a name, usually made of a few English words separated by
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475 dashes, such as @code{next-line} or @code{forward-word}. It also has a
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476 @dfn{definition}, which is a Lisp program. Only some functions can be the
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477 bindings of keys; these are functions whose definitions use
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478 @code{interactive} to specify how to call them interactively. Such
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479 functions are called @dfn{commands}, and their names are @dfn{command
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480 names}. More information on this subject will appear in the @i{XEmacs
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481 Lisp Reference Manual}.
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482
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483 The bindings between keys and functions are recorded in various tables
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484 called @dfn{keymaps}. @xref{Key Bindings}, for more information on key
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485 sequences you can bind commands to. @xref{Keymaps}, for information on
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486 creating keymaps.
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487
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488 When we say ``@kbd{C-n} moves down vertically one line'' we are
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489 glossing over a distinction that is irrelevant in ordinary use but is
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490 vital in understanding how to customize Emacs. The function
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491 @code{next-line} is programmed to move down vertically. @kbd{C-n}
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492 has this effect @i{because} it is bound to that function. If you rebind
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493 @kbd{C-n} to the function @code{forward-word} then @kbd{C-n} will move
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494 forward by words instead. Rebinding keys is a common method of
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495 customization.@refill
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496
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497 The rest of this manual usually ignores this subtlety to keep
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498 things simple. To give the customizer the information needed, we often
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499 state the name of the command that really does the work in parentheses
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500 after mentioning the key that runs it. For example, we will say that
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501 ``The command @kbd{C-n} (@code{next-line}) moves point vertically
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502 down,'' meaning that @code{next-line} is a command that moves vertically
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503 down and @kbd{C-n} is a key that is standardly bound to it.
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504
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505 @cindex variables
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506 While we are on the subject of information for customization only,
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507 it's a good time to tell you about @dfn{variables}. Often the
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508 description of a command will say, ``To change this, set the variable
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509 @code{mumble-foo}.'' A variable is a name used to remember a value.
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510 Most of the variables documented in this manual exist just to facilitate
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511 customization: some command or other part of Emacs uses the variable
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512 and behaves differently depending on its setting. Until you are interested in
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513 customizing, you can ignore the information about variables. When you
|
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514 are ready to be interested, read the basic information on variables, and
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515 then the information on individual variables will make sense.
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516 @xref{Variables}.
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