Each file contains data for a single language, and should take that language’s ISO 639-1 language designator as its name (for example, pt.xml for Portuguese). If necessary, locale-specific customizations can be provided by adding a region designator to the file name (for example, pt_BR.xml for Brazilian Portuguese).

The index files consist of index.group elements which contain sorting information on one or more characters. Index groups are listed in sort order (“specials” before numbers, numbers before the letter ‘A‘, etc), and the char.set entries they contain are also listed in sort order (uppercase before lowercase).

The best way to start editing a custom index file is by making a copy of the original from org.dita.pdf2/cfg/common/index and making changes as desired.

In order to apply a custom index definition to your publishing outputs, edit catalog.xml and uncomment the appropriate entry in the “Index configuration override entries” section.