Alyssa's Coding Journal

Introduction

This is an overview of the internal structure of EPUB 3.2 files. (Which I’ll henceforth just call ‘EPUB’, no version number specified, when not specifically contrasting with other EPUB versions.) It’s written as a followup / companion piece to my prior overview of EPUB 2.0.1 files, with similar goals in mind: to serve as a resource for programmers who want to make EPUB-generating software, as an easier-to-read (albeit less thorough) alternative to the official format specification (archive).

Like the previous summary, this one is targeted specifically at creators of EPUB-writing software, not EPUB-reading software, and will omit summaries of reader-specific requirements and of features which are deprecated or otherwise unlikely to be of relevance to creators of EPUB-writing software. For those interested in a more complete picture, see the format specification linked in the prior paragraph.

EPUB 3.2, as a format, is substantially more elaborate and feature-rich than EPUB 2.0.1 was. Moreover, even in those parts of the format which are superficially similar, many changes have been made. Thus, this summary will be very long, and will include many elements which are similar to but subtly different from those in the 2.0.1 summary.

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Introduction

This is an overview of the internal structure of EPUB 2.0.1 files. (Which I’ll henceforth call just ‘EPUB’, no version number specified, for the sake of conciseness.) My goal in writing this is to provide a useful resource for programmers who want to create programs which generate well-formed EPUB files; I intend to summarize all essential information about the format’s internal structures for that purpose, while hopefully being briefer and less intimidating to read than the format’s official specifications (archive 1, archive 2, archive 3).

While I will be going into a fair amount of detail, this is an overview, not a fully detailed exposition. In particular, if you’re designing an EPUB reader, I’d recommend looking at the official specifications instead; my summary will convey the information necessary to write well-formed EPUB files, but the format has various optional frills—deprecated features, optional but not-typically-used file format support, and so forth—which a writer doesn’t need to know how to generate but which a reader does need to know how to parse, and my summary won’t cover all of those.

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