index.on.role boolean
index.on.role Select indexterms based on role value

## Description

If non-zero, then an index element that has a role attribute value will contain only those indexterm elements with a matching role value. If an index has no role attribute or it is blank, then the index will contain all indexterms in the current scope.

If `index.on.role` is zero, then the role attribute has no effect on selecting indexterms for an index.

If you are using DocBook version 4.3 or later, you should use the type attribute instead of role on indexterm and index, and set the index.on.type to a nonzero value.