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Re: [css3-fonts] font-feature-settings syntax

From: Christopher Slye <cslye@adobe.com>
Date: Thu, 19 Apr 2012 23:31:38 -0700
CC: WWW Style <www-style@w3.org>
Message-ID: <7EA2B23F-AC12-4B0C-8ADC-89ECEB32B88D@adobe.com>
To: John Daggett <jdaggett@mozilla.com>
The second sentence in your new (and old) wording seems redundant. I would omit it, to say:

The <string> is a case-sensitive OpenType feature tag. As specified in the OpenType specification, feature tags contain four ASCII characters. Tag strings longer or shorter than four characters, or containing characters outside the U+20-7E codepoint range must be treated as invalid. User agents must not use a feature tag created by truncating or padding the string to four characters.

-Christopher


On Apr 19, 2012, at 12:33 AM, John Daggett wrote:

> The font-feature-settings in CSS3 Fonts currently has a relatively
> simple syntax, it takes a comma-delimited list of strings with an
> optional value or on/off keyword [1].  The strings represent OpenType
> tags which are defined to be 4-character ASCII strings.
> 
> Example:
> 
>  /* enable small caps and use second swash alternate */
>  font-feature-settings: "smcp", "swsh" 2;
> 
> The spec contains the following wording:
> 
>  The <string> is a case-sensitive OpenType feature tag. For it to
>  match an OpenType feature contained in a font, it must follow the
>  syntax rules for tags. As specified in the OpenType specification,
>  feature tags contain four characters. Tag strings longer than four
>  characters must be ignored, user agents must not use a feature tag
>  created by truncating the string to four characters.
> 
> This doesn't define clearly the behavior for smaller strings and
> strings containing non-ASCII codepoints.  I'd like to tighten this up
> to make it so that only four-character ASCII strings are considered
> valid, since shorter strings or strings with non-ASCII characters
> won't ever match an OpenType font feature and are most likely a typo.
> 
> I propose changing the wording above to:
> 
>  The <string> is a case-sensitive OpenType feature tag. For it to
>  match an OpenType feature contained in a font, it must follow the
>  syntax rules for these tags. As specified in the OpenType
>  specification, feature tags contain four ASCII characters. Tag
>  strings longer or shorter than four characters, or containing
>  characters outside the U+20-7E codepoint range must be treated as
>  invalid.  User agents must not use a feature tag created by
>  truncating or padding the string to four characters.
> 
> The current editor's draft also lists an issue as to whether quotes
> should be required.  I think it would be best to resolve this now and
> simply require quotes. The Webkit-prefixed version of Chrome on
> Windows doesn't require them but the IE10 Preview version does.  I
> think there was enough opposition to unquoted strings during the
> original discussion of this [2] that it would make sense to require
> quotes and remove the issue from the spec.
> 
> Regards,
> 
> John Daggett
> 
> [1] http://dev.w3.org/csswg/css3-fonts/#font-feature-settings-prop
> [2] http://lists.w3.org/Archives/Public/www-style/2011Mar/0280.html
> 
Received on Friday, 20 April 2012 06:32:10 GMT

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