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Our Texinfo source file will be called vacuum.texi and describe a fictitious vacuum command. As usual, you can enter the source using a plain-text editor:

\input texinfo @c -*-texinfo-*-

@c %**start of header

@setfilename vacuum.info

@settitle The Empty Info File

@setchapternewpage odd

@c %**end of header

This is the header of the Texinfo source. The first line is a TEX command used to input the Texinfo macros when producing printed documentation. Commands in Texinfo begin with the "at" sign, @. The @c command begins a comment; here, the comment -*-texinfo-*- is a tag that tells Emacs this is a Texinfo source file so that Emacs can set the proper major mode. (Major modes were discussed in "Tailoring Emacs" in Chapter 19.)

The comments @c %**start of header and @c %**end of header are used to denote the Texinfo header. This is required if you wish to format just a portion of the Texinfo file. The @setfilename command specifies the filename to use for the resulting Info file, @settitle sets the title of the document, and @setchapternewpage odd tells Texinfo to start new chapters on an odd-numbered page. These are just cookbook routines that should be used for all Texinfo files.

The next section of the source file sets up the title page, which is used when formatting the document using TEX. These commands should be self-explanatory:

@titlepage

@title Vacuum

@subtitle The Empty Info File

@author by Tab U. Larasa

@end titlepage

Now we move on to the body of the Texinfo source. The Info file is divided into nodes, where each node is somewhat like a "page" in the document. Each node has links to the next, previous, and parent nodes, and can be linked to other nodes as cross-references. You can think of each node as a chapter or section within the document with a menu to nodes below it. For example, a chapter-level node has a menu that lists the sections within the chapter. Each section node points to the chapter-level node as its parent. Each section also points to the previous and next section, if they exist. This is a little complicated, but will become clear when you see it in action.

Each node is given a short name. The topmost node is called Top. The @node command is used to start a node; it takes as arguments the node name, as well as the names of the next, previous, and parent nodes. As noted earlier, the next and previous nodes should be on the same hierarchical level. The parent node is the node above the current one in the node tree (e.g., the parent of Section 2.1 in a document is Chapter 2). A sample node hierarchy is depicted in Figure 20-2.

Figure 20-2. Hierarchy of nodes in Texinfo

Here is the source for the Top node:

@c Node, Next, Previous, Up

@node Top, , , (dir)

@ifinfo

This Info file is a close approximation to a vacuum. It documents

absolutely nothing.

@end ifinfo

@menu

* Overview:: Overview of Vacuum

* Invoking:: How to use the Vacuum

* Concept Index:: Index of concepts

@end menu

The @node command is preceded by a comment to remind us of the order of the arguments to @node. Here, Top has no previous or next node, so they are left blank. The parent node for Top is (dir), which denotes the systemwide Info page directory. Supposedly your Info file will be linked into the system's Info page tree, so you want the Top node to have a link back to the overall directory.

Following the @node command is an abstract for the overall document, enclosed in an @ifinfo...@end ifinfo pair. These commands are used because the actual text of the Top node should appear only in the Info file, not the TEX-generated printed document.

The @menu...@end menu commands demarcate the node's menu. Each menu entry includes a node name followed by a short description of the node. In this case, the menu points to the nodes Overview, Invoking, and Concept Index, the source for which appears later in the file. These three nodes are the three "chapters" in our document.

We continue with the Overview node, which is the