[MPEG-OTSPEC] An input on the 5th edition

[John Hudson]

On 17042023 7:59 am, 木田泰夫 wrote:
> For the 5th edition of Open Font Format, CITPC would like to clarify how it describes ‘palt’.
>
> It states, “If ‘kern’ is activated, ‘palt’ must also be activated if it exists.”.
>
> First, does this sentence represent requirements for fonts? Or does it describe requirements for font rendering and text layout/shaping engines? It needs to be clarified which interpretation is correct.

This would be a requirement or recommendation for text layout. ‘If it 
exists’ means if palt is present in the font, and I believe the intent 
is that kern and palt are intended to complement each other, so if one 
is active then the other should be also.

That said, this feature was registered by Adobe, so reflects Adobe’s 
intentions for how they planned to implement it in their own CJK layout. 
So...

> Second, in ISO/IEC, the word “MUST” represents external constraints rather than requirements specified in standards. See 7.2 in ISO/IEC Directives, Part 2. This sentence should be reformulated using “shall”, “shall not”, “may”, and so forth.

...there may be disagreement about which word is appropriate in this 
particular case. Is this a recommendation to layout implementers, or a 
requirement based on how font developers are expected to implement kern 
and palt for CJK layout?

In general, the wording of OpenType Layout feature descriptions in the 
registry is quite loose and informal, and doesn’t strictly conform to 
any conventions or directives regarding meaning of specific words. For a 
long time, there was a question whether the OTL registries were even 
formally part of the specification, or simply informational appendices.

As a general observation, I am not sure that the ISO/IEC understanding 
of ‘must’ corresponds to that I have encountered in font-related 
specifications, where it tends to represent a strong requirement, 
regardless of whether due to external constraints. The OFF standard, of 
course, began life as a direct port of Microsoft’s OpenType font format 
specification, so its use of terminology in multiple places may not 
correspond to ISO/IEC directives.

J.


-- 

John Hudson
Tiro Typeworks Ltd    www.tiro.com

Tiro Typeworks is physically located on islands
in the Salish Sea, on the traditional territory
of the Snuneymuxw and Penelakut First Nations.

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