Indexing Without Page Numbers
http://www.stc.org/confproceed/1999/PDFs/stc-117.pdf

Maislin, Seth A.
STC Proceedings
1999

Abstract:

The page number provides an intuitive context. Embedded indexing tools suffer because this context is transparent to authors. Further challenges arise from the low design priority awarded to embedding indexing tools of several applications. Hypertext-based indexing, such as on the World Wide Web, is an extreme case with difficulties ranging from a huge scope with negligible natural content, to a programming language that provides no straightforward technique for indentation.