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Re: New Thread - FVS Assignment MisMatch

From: Richard Wordingham <richard.wordingham@ntlworld.com>
Date: Thu, 6 Aug 2015 08:52:12 +0100
To: "public-i18n-mongolian@w3.org" <public-i18n-mongolian@w3.org>
Message-ID: <20150806085212.3a91311b@JRWUBU2>
On Thu, 6 Aug 2015 02:37:06 +0000
Greg Eck <greck@postone.net> wrote:

> I am not quite clear on your reply. If we deal only with the textual
> specification, are you saying that the actual current spec for U+1820
> should look like this with the "NotUsed" lines actually in the spec?
> I am not talking about the implementation at this point.
> 
> ISOLATE
> 1820+NoFVS	SpecificationDescription
> 1820+FVS1	SpecificationDescription
> 1820+FVS2	NotUsed
> 1820+FVS3	NotUsed
> INITIAL
> 1820+NoFVS	SpecificationDescription
> 1820+FVS1	NotUsed
> 1820+FVS2	NotUsed
> 1820+FVS3	NotUsed
> MEDIAL
> 1820+NoFVS	SpecificationDescription
> 1820+FVS1	SpecificationDescription
> 1820+FVS2	SpecificationDescription
> 1820+FVS3	NotUsed
> FINAL
> 1820+NoFVS	SpecificationDescription
> 1820+FVS1	SpecificationDescription
> 1820+FVS2	NotUsed
> 1820+FVS3	NotUsed

Human language is horribly ambiguous.

1) The 'NotUsed' entries are implicit.  You don't need to list them in
the specification.

2) The Unicode Specification says that 1820+FVS3 shall be treated the
same way as 1820+NoFVS, for it is 'NotUsed'.  However, you shouldn't
believe anything you read in the Unicode Specification.

3) As 1820+FVS2 is defined for 'Medial', it is not clear what is allowed
to happen for isolated, initial and final.  The Unicode Standard 7.00
reads, in Chapter 13:

"These format characters normally have no visual appearance. When
required, a free variation selector immediately follows the base
character it modifies. This combination of base character and variation
selector is known as a standardized variant. The table of standardized
variants, StandardizedVariants.txt, in the Unicode Character Database
exhaustively lists all currently defined standardized variants. All
combinations not listed in the table are unspecified and are reserved
for future standardization; no conformant process may interpret them as
standardized variants. Therefore, any free variation selector not
immediately preceded by one of their defined base characters will be
ignored."

The reasonable interpretation is that 1820+FVS2 should be treated the
same as 1820+NoFVS in isolated, initial and final positions.

4) It would be nice to see 'specification description' in Richard
Ishida's document for +NoFVS.  It doesn't tell us when an FVS is
unnecessary.

Richard.


> 
> Greg







> 
> 
> -----Original Message-----
> From: Richard Wordingham [mailto:richard.wordingham@ntlworld.com] 
> Sent: Thursday, August 6, 2015 10:23 AM
> To: Greg Eck <greck@postone.net>
> Cc: jrmt@almas.co.jp; public-i18n-mongolian@w3.org
> Subject: Re: New Thread - FVS Assignment MisMatch
> 
> On Thu, 6 Aug 2015 01:56:08 +0000
> Greg Eck <greck@postone.net> wrote:
> 
> > If we take one example from the font comparator site 
> > (http://r12a.github.io/scripts/mongolian/variants ) and look at
> > U+1820. We see that Isolate+FVS1 is specified. Isolate+FVS2 AND
> > Isolate+FVS3 are not specified as they are "don't care conditions".
> > These two sequences are left to the judgment of the font designer
> > to handle.
> 
> No.
> 
> <U+1820, FVS3> must be treated the same as U+1820, for the variation
> sequence is not defined.  Once <U+1820, FVS2> ceases to be specified
> for any position, then the same will apply to <U+1820, FVS2>.
> 
> It is not clear what should happen if only some positional variants
> are defined for a variation sequence.
> 
> Richard.
Received on Thursday, 6 August 2015 07:52:47 UTC

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