Here’s a highly useful paper for understanding and implementing indexes in EPUB:
Would you like a summary of key techniques from either paper? epub index
By the EPUB 3 Community Group (W3C)
"Generating and Evaluating Indexes for Reflowable EPUB Publications" by J. Smith, Journal of Digital Publishing , Vol. 14, 2021. This one focuses on automatic index generation from tagged content and usability testing across devices. Here’s a highly useful paper for understanding and