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1 @node Startup Paths, Packages, Command Switches, Top
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2 @comment node-name, next, previous, up
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3 @section How XEmacs finds Directories and Files
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4
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5 @cindex startup paths
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6 @cindex directories
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7
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8 XEmacs deals with a multitude of files during operation. These files
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9 are spread over many directories, and XEmacs determines the location of
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10 most of these directories at startup and organizes them into various
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11 paths. (A @dfn{path},
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12 @cindex path
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13 for the purposes of this section, is simply a list of directories which
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14 XEmacs searches successively in order to locate a file.)
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15
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16 @subsection XEmacs Directory Hierarchies
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17 @cindex hierarchies
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18 @cindex directory hierarchies
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19
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20 Many of the files XEmacs looks for are located within the XEmacs
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21 installation itself. However, there are several views of what actually
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22 constitutes the "XEmacs installation": XEmacs may be run from the
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23 compilation directory, it may be installed into arbitrary directories,
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24 spread over several directories unrelated to each other. Moreover, it
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25 may subsequently be moved to a different place. (This last case is not
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26 as uncommon as it sounds. Binary kits work this way.) Consequently,
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27 XEmacs has quite complex procedures in place to find directories, no
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28 matter where they may be hidden.
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29
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30 XEmacs will always respect directory options passed to @code{configure}.
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31 However, if it cannot locate a directory at the configured place, it
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32 will initiate a search for the directory in any of a number of
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33 @dfn{hierarchies} rooted under a directory which XEmacs assumes contain
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34 parts of the XEmacs installation; it may locate several such hierarchies
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35 and search across them. (Typically, there are just one or two
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36 hierarchies: the hierarchy where XEmacs was or will be installed, and
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37 the one where it is being built.) Such a directory containing a
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38 hierarchy is called a @dfn{root}.
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39 @cindex root of a hierarchy
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40 Whenever this section refers to a directory using the shorthand
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41 @code{<root>}, it means that XEmacs searches for it under all
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42 hierarchies XEmacs was able to scrounge up. In a
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43 running XEmacs, the hierarchy roots are stored in the variable
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44 @code{emacs-roots}.
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45 @vindex emacs-roots
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46
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47 @subsection Package Hierarchies
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48 @cindex package hierarchies
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49
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50 Many relevant directories and files XEmacs uses are actually not part of
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51 the core installation. They are part of any of the many packages
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52 usually installed on top of an XEmacs installation. (@xref{Packages}.)
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53 Hence, they play a prominent role in the various paths XEmacs sets up.
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54
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55 XEmacs locates packages in any of a number of package hierarchies.
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56 Package hierarchies fall into three groups: @dfn{early}, @dfn{late},
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57 and @dfn{last},
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58 @cindex early package hierarchies
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59 @cindex late package hierarchies
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60 @cindex last package hierarchies
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61 according to the relative location at which they show
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62 up in the various XEmacs paths. Early package hierarchies are at the
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63 very front, late ones somewhere in the middle, and last hierarchies are
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64 (you guessed it) last.
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65
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66 By default, XEmacs expects an early package hierarchy in the
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67 subdirectory @file{.xemacs/xemacs-packages} of the user's home
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68 directory.
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69
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70 Moreover, XEmacs expects late hierarchies in the subdirectories
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71 @file{site-packages}, @file{mule-packages}, and @file{xemacs-packages}
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72 (in that order) of the @file{<root>/lib/xemacs} subdirectory of one of
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73 the installation hierarchies. (If you run in-place, these are direct
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74 subdirectories of the build directory.) Furthermore, XEmacs will also
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75 search these subdirectories in the @file{<root>/lib/xemacs-<VERSION>}
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76 subdirectory and prefer directories found there.
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77
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78 By default, XEmacs does not have a pre-configured last package
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79 hierarchy. Last hierarchies are primarily for using package hierarchies
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80 of outdated versions of XEmacs as a fallback option. For example, it is
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81 possible to run XEmacs 21 with the 20.4 package hierarchy as a last
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82 hierarchy.
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83
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84 It is possible to specify at configure-time the location of the various
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85 package hierarchies with the @code{--package-path} option to configure.
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86 @cindex package path
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87 The early, late, and last components of the package path are separated
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88 by double instead of single colons. If all three components are
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89 present, they locate the early, late, and last package hierarchies
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90 respectively. If two components are present, they locate the early and
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91 late hierarchies. If only one component is present, it locates the
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92 late hierarchy. At run time, the package path may also be specified via
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93 the @code{EMACSPACKAGEPATH} environment variable.
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94
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95 An XEmacs package is laid out just like a normal installed XEmacs lisp
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96 directory. It may have @file{lisp}, @file{etc}, @file{info}, and
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97 @file{lib-src} subdirectories. XEmacs adds these at appropriate places
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98 within the various system-wide paths.
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99
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100 There may be any number of package hierarchy directories.
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101
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102 @subsection Directories and Paths
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103 @cindex paths
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104
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105 Here is a list of the various directories and paths XEmacs tries to
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106 locate during startup. XEmacs distinguishes between directories and
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107 paths specific to @dfn{version}, @dfn{site}, and @dfn{architecture}
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108 when looking for them.
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109
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110 @table @code
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111 @item version-specific
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112 @cindex version-specific directories
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113 directories are specific to the version of XEmacs they belong to and
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114 typically reside under @file{<root>/lib/xemacs-<VERSION>}.
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115 @item site-specific
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116 @cindex site-specific directories
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117 directories are independent of the version of XEmacs they belong to and
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118 typically reside under @file{<root>/lib/xemacs}
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119 @item architecture-specific
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120 @cindex architecture-specific directories
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121 directories are specific both to the version of XEmacs and the
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122 architecture it runs on and typically reside under
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123 @file{<root>/lib/xemacs-<VERSION>/<ARCHITECTURE>}.
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124 @end table
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125
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126 During installation, all of these directories may also reside directly
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127 under @file{<root>}, because that is where they are in the XEmacs tarball.
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128
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129 If XEmacs runs with the @code{-debug-paths} option (@pxref{Command
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130 Switches}), it will print the values of these variables, hopefully
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131 aiding in debugging any problems which come up.
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132
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133 @table @code
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134
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135 @item lisp-directory
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136 @vindex lisp-directory
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137 Contains the version-specific location of the Lisp files that come with
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138 the core distribution of XEmacs. XEmacs will search it recursively to a
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139 depth of 1 when setting up @code{load-path}.
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140
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141 @item load-path
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142 @vindex load-path
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143 Is where XEmacs searches for XEmacs Lisp files with commands like
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144 @code{load-library}.
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145 @findex load-library
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146 It contains the package lisp directories (see further down) and the
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147 version-specific core Lisp directories. If the environment variable
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148 @code{EMACSLOADPATH} is set at startup, its directories are prepended to
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149 @code{load-path}.
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150 @vindex EMACSLOADPATH
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151
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152 @item Info-directory-list
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153 @vindex Info-directory-list
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154 Contains the location of info files. (See @ref{(info)}.) It contains
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155 the package info directories and the version-specific core
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156 documentation. Moreover, XEmacs will add @file{/usr/info},
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157 @file{/usr/local/info} as well as the directories of the environment
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158 variable @code{INFOPATH}
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159 @vindex INFOPATH
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160 to @code{Info-directory-list}.
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161
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162 @item exec-directory
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163 @vindex exec-directory
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164 Is the directory of architecture-dependent files that come with XEmacs,
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165 especially executable programs intended for XEmacs to invoke.
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166
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167 @item exec-path
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168 @vindex exec-path
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169 Is the path for executables which XEmacs may want to start. It contains
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170 the package executable paths as well as @code{exec-directory}, and the
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171 directories of the environment variables @code{PATH}
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172 @vindex PATH
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173 and @code{EMACSPATH}.
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174 @vindex EMACSPATH
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175
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176 @item doc-directory
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177 @vindex doc-directory
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178 Is the directory containing the architecture-specific @file{DOC} file
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179 that contains documentation for XEmacs' commands.
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180
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181 @item data-directory
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182 @vindex data-directory
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183 Is the version-specific directory that contains core data files XEmacs uses.
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184 It may be initialized from the @code{EMACSDATA}
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185 @vindex EMACSDATA
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186 environment variable.
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187
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188 @item data-directory-list
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189 @vindex data-directory-list
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190 Is the path where XEmacs looks for data files. It contains package data
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191 directories as well as @code{data-directory}.
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192
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193 @end table
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