I am a reader that uses indexes when a document provides them. My best reference textbooks contain excellent indexes, and that is indeed part of why I consider them my best references: because finding information that I am looking for in them is fast and accurate.
Because I know what a huge tool indexes can be for the reader, I too like to provide an excellent index when the work will be used as a reference. Thus, I was delighted to find that Dr.Explain supports the creation of a 1-, 2- and 3-level index (or more levels if needed), and not only that, but doing so with Dr.Explain is just as efficient as the best indexing software tools I have ever used, and in some cases, more so.
For the reader who is interested in learning this craft, I created an entire article about how to create an index for a large help file, document or book.