[sieve]

epub is overkill for a vast majority of books.

A format that only supported

- headings

- paragraphs

- emphasis (bold/italics)

- bullets

- inline images

is good enough. A simple container with a TOC pointing to text blocks/files within it that can be processed very cheaply.

Unfortunately, with something like epub, you lose all the simplicity because you want to support every single feature even if rarely used.