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D2 Coding wiki

Notes for people who maintain the font: how the files are put together, the decisions behind them, and how to change a shipped binary without breaking anything else.

User documentation lives in the repository, not here:

• README.md: download, install, coverage
• CHANGELOG.md: what changed in each version
• RELEASE.md: the release procedure
• sources/README.md: what the UFO sources are and are not
• Specimen page: rendering tests in the browser

Maintainer notes

1. Font file primer: the tables and terms that come up in issues and commits (glyph IDs, cmap, hmtx, GSUB, calt and liga, hinting, ppem).
2. Width policy: the 1:2 grid, East Asian Width, and which characters are one or two columns.
3. Editing the binaries: how to patch the shipped TTFs with fontTools, keep the UFO sources in step, and avoid the traps that rewrite bytes you did not mean to touch.
4. Verifying a change: HarfBuzz, FreeType and browser checks, with snippets.
5. Recurring reports: questions that keep coming back, with the answer and the issue that settled it.

Open Font License points at the license in the repository.