[mpeg-OTspec] Updated 4th edition working draft available for review

[John Hudson]

My concern is that the proposed wording relaxes the requirement that the language system count be zero, but then states that implementations are not required to do anything with any language systems mapped to the DFLT script. So it's basically saying 'Yes, you can have an unreliable mechanism'.

I would rather the wording say something to the effect that language systems mapped to the DFLT script tag should be treated the same as language systems mapped to any other script tag, rather than suggesting, as the proposed wording does, that the DFLT script remains a special case with regard to language systems. Implementations may still fail to support language system tags in various ways — as they do already —, but should do so consistently regardless of whether the script tag is specific or DFLT.

JH


Sent from my iPad

> On Mar 31, 2017, at 5:34 PM, Peter Constable <petercon at microsoft.com> wrote:
> 
> John:
>  
> Can you clarify for me what specifically about which part of the wording concerns you.
>  
> I think I’ve stayed consistent with what the spec was already saying about DFLT script tag in general, and only stated it (I think) more clearly:
>  
> “The 'DFLT' Script table should be used if there is not an explicit entry for the script being formatted.”
>  
> The key change has been to relax the constraint that LangSysCount “must be equal to 0”. “A font is permitted…” is implied if that constraint has been relaxed.
>  
> Is this concern with this?
> “An application should use a 'DFLT' script table … if the text does not have a specific script (for example, it contains only symbols or punctuation).”
> If so, I could work on that.
>  
> Peter
>  
> From: John Hudson [mailto:john at tiro.ca] 
> Sent: Friday, March 31, 2017 6:56 AM
> To: Peter Constable <petercon at microsoft.com>
> Cc: Martin Hosken <martin_hosken at sil.org>; Levantovsky, Vladimir <Vladimir.Levantovsky at monotype.com>; mpeg-OTspec at yahoogroups.com
> Subject: Re: [mpeg-OTspec] Updated 4th edition working draft available for review
>  
> Peter, I'm a bit concerned that this wording makes some assumptions about how implementations use the DFLT script tag, without those implementations being specified anywhere. [Well, nothing new in that: this is true of OpenType Layout in general.] So, for example, I've seen DFLT used by Adobe to process script=common characters such as the Indic danda and double danda from the Unicode Devanagari block, which are also used by other Indian scripts. If one wanted to make a pan-Indic font with script-specific forms of danda, the only way to do so within that implementation would be via language system under the DFLT script tag. Of course, the case can be made that such an implementation is wrong, but sans an implementation spec, I wonder about the wisdom of specifying constraints in the format spec.
>  
> JH
> 
> 
> Sent from my iPad
> 
> On Mar 31, 2017, at 5:48 AM, Peter Constable petercon at microsoft.com [mpeg-OTspec] <mpeg-OTspec-noreply at yahoogroups.com> wrote:
> 
> A font is permitted to have a 'DFLT' script table with non-default language system tables, and an application
>         may use features associated with one of these if the the 'DFLT' script table is applicable (no script table
>         is present for the specific script), and if one of the particular language systems is specified. Applications
>         are not required to support use of a non-default language system table that is associated with 'DFLT' script,
>         however, and fonts should not depend on this configuration being supported.
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