Nesting index entries

The technique of nesting indexterm elements can produce multi-level indexes in output documents.

You can created multi-level (secondary and tertiary) indexes by nesting indexterm elements.

For example, the mark-up:
<indexterm>EJ25 engine
  <indexterm>performance</indexterm>
</indexterm>
may produce, in a page layout output, and index entry of:

EJ25 engine
    performance .................... 15

The page reference is applied to the innermost term (in the example, "performance") only.

An example of a more complex index result is:

EJ25 engine
    dimensions .................... 72
    maintenance .................... 33
    performance .................... 15
    specifications .................... 49

In a hypertext document that supports multi-level indexes, the same example might be displayed as:

Screen capture showing a multi-level index in a Help system

You should avoid nesting index entries to more than three levels. In most cases, one or two levels will provide sufficient scope for a comprehensive and easy-to-navigate index.

If you have a number of secondary entries belonging to the same parent entry, such as "EJ25 engine, performance" and "EJ25 engine, torque", the secondary entries can either be nested under the same parent entry, or structured separately.

In other words,
<indexterm>EJ25 engine
  <indexterm>performance</indexterm>
  <indexterm>torque</indexterm>
</indexterm>
is equivalent to
<indexterm>EJ25 engine
  <indexterm>performance</indexterm>
</indexterm>
<indexterm>EJ25 engine
  <indexterm>torque</indexterm>
</indexterm>