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Format

FAB2 Book Container

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Summary

Name
FAB2 Book Container
Version
0.2
Identifiers
  • PUID: fmt/2108
  • MIME: application/vnd.fabylon.book
Format type
  • Page Description
  • Word Processor
Description
A container for digital books that stores the book as typographic data, unlike other alternatives that store books as web documents inside an archive. The container has no scripting and no executable content. Page records carry resolved line geometry, so line breaks and optical margins are decided once when the book is typeset rather than recomputed on the reading device. The signature contains an initial 16 byte magic byte header, after which it holds two little-endian unsigned 32-bit lengths, a Zstandard-compressed JSON manifest, and a chunk arena containing one compressed page block and the book's assets.
Note
Specification: https://www.google.com/url?q=https://fabylon.net/fab/specification/&source=gmail&ust=1787034048114000&sa=E Related software: Fabylon Bookmaker — writes .fab — https://www.google.com/url?q=https://www.martijnbenders.nl/bookmaker/&source=gmail&ust=1787034048114000&sa=E Fabylon Reader — reads .fab — https://www.google.com/url?q=https://fabylon.net/fabreader/&source=gmail&ust=1787034048114000&sa=E
File extensions
fab
Submitted by
Fabylon / Fabylon
Developed by
Fabylon / Fabylon
Supported by
Fabylon / Fabylon

Internal signatures

FAB2 Book Container

Description
BOF; Offset: 0; Magic Bytes: 'ASCII FABYLON_BOOK_02!'
Provenance
The signature is fixed and always at offset 0 with no preceding bytes. The generation number is inside the magic string itself, so an unknown future generation can be rejected before parsing. An earlier generation used the signature FABYLON_REALM_01 (hex 46 41 42 59 4C 4F 4E 5F 52 45 41 4C 4D 5F 30 31) with a different internal structure; it is still readable by current software but is no longer written.

Byte sequences

Min Frag Length
Absolute from BOF
Offset
0
Max offset
0
Byte Sequence
464142594C4F4E5F424F4F4B5F303221
Endianness
None

Changelog

  • V125

    Release date
    7 September 2026

    • Added format

      FAB2 Book Container 0.2: Full entry added. Submitted by Fabylon.

    • Added signature

      FAB2 Book Container 0.2: Signature researched and samples provided by Fabylon.