[MPEG-OTSPEC] VARC issues with the published OFF 5th ed

[Dave Crossland]

Thanks for flagging these, Behdad. Glad to see you're cross-checking the
implementations already.

Vlad, sounds like this is enough to Kickoff a 1st amendment :) if so, what
would you for cast as an overall end to end timeline?


-- 
[image: GDP logo]


Dave Crossland

Font Expert

Google Design Platform



On Fri, Oct 2, 2026, 3:30 PM Behdad Esfahbod <behdad at behdad.org> wrote:

> Hello everyone,
>
> Thank you, Vlad, and everyone else who worked in the past four years to
> get the boring-expansion proposals into the ISO OFF 5th ed.
>
> Since the PDF became freely available on Monday, I've been busy
> cross-checking my implementations against the spec. Generally things are
> holding up well, but unfortunately I discovered three issues in the VARC
> table that I recommend fixing in the spec. Details and recommendation in
> the github issues:
>
>
> *1. VARC ConditionList: restore omitted uint32 conditionCount*
> This one is was lost in translation from my working design to the ISO
> proposal. It's currently impossible to implement the ISO spec, because it
> defines an array without defining its length anywhere:
>
>   https://github.com/harfbuzz/boring-expansion-spec/issues/176
>
> *2. VARC: make SparseVariationRegion axis offsets table-relative and
> correct its designation*
>
> This was was a mistake from the review modifications of the table format
> to promote a struct to a table, but this was not done properly. Offsets
> should be relative to the beginning of their table, not the grandparent
> table as currently speced.
>
>   https://github.com/harfbuzz/boring-expansion-spec/issues/177
>
> *3. VARC: Remove the exception to ordinary LSB/origin alignment for
> components*
>
> This is a design leftover from when I had encoded the variable-composites
> in the `glyf` table. In that design, the recommendation made sense. In a
> separate `VARC` table, it doesn't, and hinders implementation. This change
> wouldn't affect properly-made fonts (lsb=xMin).
>
>   https://github.com/harfbuzz/boring-expansion-spec/issues/173
>
>
> That's it for now. I will be spending a lot more time with the spec, but I
> don't expect other major issues to arise.
>
> Thanks,
> behdad
> http://behdad.org/
>
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