Legal posture

Research memo, August 2026. This records why the project believes its activity is lawful, what remains genuinely gray, and which decisions were taken on that basis. It is research, not legal advice.

The activity: settled ground

Reverse-engineering a file format for interoperability — shipping no vendor code, circumventing no protection measure — is the best-protected category of reverse engineering in software-IP law:

• US: intermediate copying for interoperability is fair use — Sega v. Accolade, 977 F.2d 1510 (9th Cir. 1992); Sony v. Connectix, 203 F.3d 596 (9th Cir. 2000). Reimplementing an interface surface for a new platform is fair use — Google v. Oracle, 593 U.S. 1 (2021). Systems and methods are outside copyright — 17 U.S.C. §102(b); facts are free — Feist v. Rural, 499 U.S. 340 (1991); functionally dictated material merges — Lexmark v. Static Control, 387 F.3d 522 (6th Cir. 2004).
• EU, directly on point: data file formats are not protected expression of a program — SAS Institute v. World Programming, C-406/10 (CJEU 2012). Observation rights cannot be waived by contract and decompilation for interoperability is permitted — Directive 2009/24/EC Arts. 5–6, with Art. 8 voiding contrary contract terms; reaffirmed in Top System, C-13/20 (CJEU 2021).
• DMCA §1201 is out of frame by design: iWork documents in this library's path are unencrypted zip + Snappy + protobuf; the descriptors sit unencrypted in the binaries; and password-protected documents are refused (EncryptedDocumentError). Even where §1201 applies, §1201(f)(3) expressly permits sharing interoperability information. This refusal is a deliberate, load-bearing property — keep it.

This project's pattern is stronger than the winning defendants' in every case above: most knowledge comes from black-box measurement of documents (the method Wine mandates), and the published artifact contains no Apple code at all.

The two gray items, and the decisions taken

1. The vendored .proto dumps. The schemas under proto/ were recovered from application binaries by third-party projects and have been continuously public since 2013 (obriensp/iWorkFileFormat) and 2021 (masaccio/numbers-parser); this repo redistributes their bytes with commit-pinned provenance. Their content — names, numbers, types — is a set of facts about the wire format (Feist, merger, §102(b); SAS in the EU), but no court has ruled on dumped descriptors as such, a US breach-of-contract theory against an extractor exists in some circuits (Bowers v. Baystate; Davidson v. Jung — against; Vault v. Quaid — preempted; EU: voided by Art. 8), and EU Art. 6(2)(b) limits sharing decompilation-derived information to what interoperability needs (these files are the compiled-in input of src/proto/vendored.ts, which is that). Decision: keep shipping the dumps with the no-copyright-claimed notice in THIRD-PARTY-NOTICES.md; the fallback, should it ever be needed, is regenerating schema text from this project's own measured tables and shipping only that — the SheetJS/libetonyek pattern.

2. The name — chosen to stay clear of Apple's marks.cupertino-files is a city name, not an Apple mark, with strong precedent in Flutter's cupertino package — Apple-design widgets shipped by Google, unchallenged for years. The caution is deliberate: peer projects have used Apple marks in their names descriptively for over a decade without enforcement (iWorkFileFormat 2013, keynote-parser 2019, numbers-parser 2021), but Apple has C&D'd open-source names before (iPodder → Juice, 2005), and npm's dispute policy sides with trademark holders (kik, 2016). Apple's marks (iWork, Pages, Numbers, Keynote, Creator Studio) therefore appear only in prose and metadata describing what the library interoperates with — the squarely protected nominative use (New Kids, Toyota v. Tabari). Names leading with Apple's house mark or the live Creator Studio brand were rejected as strictly worse.

Apple's observed enforcement line

Twelve to eighteen years of directly comparable projects — the three iWork parsers above, SheetJS, libetonyek inside LibreOffice, and libimobiledevice — with no takedown, C&D or suit found against any iWork format project, ever. What Apple does act on: leaked verbatim source (iBoot 2018; the 2025 apps.apple.com purge), commercial replication shipping Apple's software (Psystar), and names tracking its device brands. The one time Apple publicly tested the interop-RE line (OdioWorks, iTunesDB, 2009), it withdrew in writing after EFF sued. Apple v. Corellium ended with fair use affirmed for far more invasive copying than anything here. GitHub's post-youtube-dl DMCA process (technical + legal review, counter-notice, reinstatement) is the backstop, and this repo's provenance tables are the counter-notice exhibit.

License

MIT, kept deliberately. It satisfies the goals — OSI-approved, maximally permissive, battle-tested warranty and liability disclaimer, derivative- and commercial-friendly — and matches every direct peer. Apache-2.0's extra liability language buys nothing real here: its patent grant binds only contributors (the realistic patent holder for a format library would never be one), and it costs GPLv2-only compatibility, which matters for a library meant to be embedded anywhere. If corporate contributors arrive, dual MIT OR Apache-2.0 adds contributor-patent hygiene without losing reach. Public-domain-style licenses (0BSD, Unlicense) were rejected: attribution chains are this project's spine, and jurisdictional public-domain problems are real.

Mixed-content structure: root LICENSE (MIT) for the project's own work; THIRD-PARTY-NOTICES.md (shipped in the npm artifact) for the recovered schemas and redistributed fixtures; LICENSES/ with full MIT, Apache-2.0 and MPL-2.0 texts; REUSE.toml declaring per-directory licensing without editing byte-fidelity-critical files.

Sources

Primary: the cases and statutes linked inline above; Apple, Guidelines for Using Apple Trademarks; Directive 2009/24/EC; 17 U.S.C. §§102, 107, 512, 1201; EFF Coders' Rights Reverse Engineering FAQ; GitHub DMCA takedown policy and the youtube-dl reinstatement; npm disputes policy. Peer-practice evidence: the repositories of obriensp/iWorkFileFormat, psobot/keynote-parser, masaccio/numbers-parser, SheetJS, libetonyek, libimobiledevice, Asahi Linux (copyright & RE policy), Wine (clean-room policy), Samba (PFIF).