Use an appropriate level of detail in the table of contents

Information is often subdivided to many levels, with headings for each subdivision. Such a structure is useful to show a hierarchy of topics, but you do not need to include every heading of every subdivision in the table of contents. This practice usually produces a long table of contents that makes general subjects harder to find, and hides rather than reveals the organization of the information. A table of contents should provide more than the highest level of headings, but allow users to easily see the top-level hierarchy.

For Web documents such as PDF files that display the contents in a separate, scrollable frame, using expandable sections gives you the flexibility of including the lowest level of headings. Users can see at a glance the top-level headings, and choose to see lower-level headings.