Texinfo documents most usefully have a double structure, reflecting the double purposes of printed and online output. For printed output (DVI, PDF, …), with physical pages, there are chapters, sections, subsections, etc. For online output (Info, HTML, …), with interactive navigation and no physical pages, there are so-called “nodes”.
Typically, the sectioning structure and the node structure are completely parallel, with one node for each chapter, section, etc., and with the nodes following the same hierarchical arrangement as the sectioning. Thus, if a node is at the logical level of a chapter, its child nodes are at the level of sections; similarly, the child nodes of sections are at the level of subsections.
Each node has a name, and contains the discussion of one topic. Along with the text for the user to read, each node also has pointers to other nodes, identified in turn by their own names. Info readers display one node at a time, and provide commands for the user to move to related nodes. The HTML output can be similarly navigated.
The names of child nodes are listed in a menu within the parent node; for example, a node corresponding to a chapter would have a menu of the sections in that chapter. The menus allow the user to move to the child nodes in a natural way in the online output.
In addition, nodes at the same level are formed into a chain with ‘Next’ and ‘Previous’ pointers. As you might imagine, the ‘Next’ pointer links to the next node (section), and the ‘Previous’ pointer links to the previous node (section). Thus, for example, all the nodes that are at the level of sections within a chapter are linked together, and the order in this chain is the same as the order of the children in the menu of parent chapter. 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.
In addition to menus and ‘Next’, ‘Previous’, and ‘Up’ pointers, Texinfo provides pointers of another kind for cross references, that can be sprinkled throughout the text. This is usually the best way to represent links that do not fit a hierarchical structure.
Although it is technically possible to create Texinfo documents with only one structure or the other, or for the two structures not to be parallel, or for either the sectioning or node structure to be abnormally formed, etc., this is not at all recommended. To the best of our knowledge, all the Texinfo manuals currently in general use do follow the conventional parallel structure.