The text in manuals is organized into a hierarchy. Headings are used to label chunks of the text as well as identify their levels in the hierarchy. For example, in a manual modularized at the 2nd-level, the first level of the hierarchy consists of the chapters, and the second level consists of the sections. Within each section, the text is broken down further into sub-sections and sub-sub-sections. Modules normally have no more than four levels of headings associated with them. Avoid the temptation to use more levels—it makes the structure too complex for easy use.
To reinforce the text hierarchy, each level of heading is given a set of attributes that distinguish it visually from other headings. Look at the headings used in this guidebook. For more information on heading attributes, see Chapter 4.