An Info file is a Texinfo file formatted so that the Info documentation
reading program can operate on it. (
texinfo-format-buffer are two commands that convert a Texinfo file
into an Info file.)
Info files are divided into pieces called nodes, each of which contains the discussion of one topic. Each node has a name, and contains both text for the user to read and pointers to other nodes, which are identified by their names. The Info program displays one node at a time, and provides commands with which the user can move to other related nodes.
Each node of an Info file may have any number of child nodes that describe subtopics of the node's topic. The names of child nodes are listed in a menu within the parent node; this allows you to use certain Info commands to move to one of the child nodes. Generally, an Info file is organized like a book. If a node is at the logical level of a chapter, its child nodes are at the level of sections; likewise, the child nodes of sections are at the level of subsections. All the children of any one parent are linked together in a bidirectional chain of `Next' and `Previous' pointers. The `Next' pointer provides a link to the next section, and the `Previous' pointer provides a link to the previous section. This means that all the nodes that are at the level of sections within a chapter are linked together. Normally the order in this chain is the same as the order of the children in the parent's menu. Each child node records the parent node name as its `Up' pointer. The last child has no `Next' pointer, and the first child has the parent both as its `Previous' and as its `Up' pointer.(2)
The book-like structuring of an Info file into nodes that correspond to chapters, sections, and the like is a matter of convention, not a requirement. The `Up', `Previous', and `Next' pointers of a node can point to any other nodes, and a menu can contain any other nodes. Thus, the node structure can be any directed graph. But it is usually more comprehensible to follow a structure that corresponds to the structure of chapters and sections in a printed book or report.
In addition to menus and to `Next', `Previous', and `Up' pointers, Info provides pointers of another kind, called references, that can be sprinkled throughout the text. This is usually the best way to represent links that do not fit a hierarchical structure.
Usually, you will design a document so that its nodes match the structure of chapters and sections in the printed output. But there are times when this is not right for the material being discussed. Therefore, Texinfo uses separate commands to specify the node structure for the Info file and the section structure for the printed output.
Generally, you enter an Info file through a node that by convention is called `Top'. This node normally contains just a brief summary of the file's purpose, and a large menu through which the rest of the file is reached. From this node, you can either traverse the file systematically by going from node to node, or you can go to a specific node listed in the main menu, or you can search the index menus and then go directly to the node that has the information you want.
If you want to read through an Info file in sequence, as if it were a printed manual, you can get the whole file with the advanced Info command g* RET. (See Info file `info', node `Expert'.)
The `dir' file in the `info' directory serves as the departure point for the whole Info system. From it, you can reach the `Top' nodes of each of the documents in a complete Info system.