- Format v3: optional gzip (Preferences > File Handling > Use Compression, or
document.save {compress}); compressed files open by their magic bytes, legacy
ones too.
- Every file write goes to a temporary file renamed over the target (engine
writes and the desktop app's writer), so a failed save keeps the old file.
- Only the images the document uses are written.
- Document keys from newer versions are kept (Document.extra, flattened).
- Assigned colour profiles are a real field (Document.color_profiles),
migrated from unknown.colorProfiles on load.
- document.save {version: 1|2} writes files older versions open; {preview}
embeds a PNG of the first artboard of at most 256 px.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
65cdc45ed9