For Info to work, the `info' directory must contain a file that serves as a top level directory for the Info system. By convention, this file is called `dir'. (You can find the location of this file within Emacs by typing C-h i to enter Info and then typing C-x C-f to see the pathname to the `info' directory.)
The `dir' file is itself an Info file. It contains the top level menu for all the Info files in the system. The menu looks like this:
* Menu: * Info: (info). Documentation browsing system. * Emacs: (emacs). The extensible, self-documenting text editor. * Texinfo: (texinfo). With one source file, make either a printed manual using TeX or an Info file. ...
Each of these menu entries points to the `Top' node of the Info file that is named in parentheses. (The menu entry does not need to specify the `Top' node, since Info goes to the `Top' node if no node name is mentioned. See section Referring to Other Info Files.)
Thus, the `Info' entry points to the `Top' node of the `info' file and the `Emacs' entry points to the `Top' node of the `emacs' file.
In each of the Info files, the `Up' pointer of the `Top' node refers
back to the
dir file. For example, the line for the `Top'
node of the Emacs manual looks like this in Info:
File: emacs Node: Top, Up: (DIR), Next: Distrib
(Note that in this case, the `dir' file name is written in upper case letters--it can be written in either upper or lower case. Info has a feature that it will change the case of the file name to lower case if it cannot find the name as written.)
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