[MPEG-OTSPEC] Rules for cubic bits in glyf flags include undefined behaviour for some configurations

[Laurence Penney]

I agree with Bob, that (paraphrasing) "all switches must either be on or off" is ambiguous and we should fix it.

I propose:

"In any sequence of off-curve points between two on-curve points (with wrap-around), either all points in the sequence have the CUBIC flag set, or all points in the sequence have the CUBIC flag clear."

(I’m slightly uncomfortable using parentheses like this, but that’s a separate issue.)

- Laurence

> On 4 Oct 2023, at 00:05, Bob Hallissy <bob_hallissy at sil.org> wrote:
> 
> 
> 
> On 9/23/2023 1:02 PM, Laurence Penney wrote:
>> All the off-curve points between two on-curve points (with wrap-around) must either
>> have the CUBIC flag clear, or have the CUBIC flag set.
> 
> I find the above ambiguous -- my first reaction was "well the CUBIC flag is binary so of course they will all have the CUBIC flag either set or clear. duh."   I realized later what (I think) was trying to be said is that they must all agree, i.e., all set or all clear. 
> 
> Also the statement is ambiguous about whether it applies to arbitrary pairs of on-curve points or not.
> 
> Could this be worded more clearly, maybe:
> Consecutive off-curve points between two on-curve points (with wrap-around) must have the same CUBIC flag value.
> 
> Bob
> 
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