Re: [css-fonts] Conflicting tags in font-feature-settings

On Wed, Mar 16, 2016 at 5:02 AM, Jonathan Kew <jfkthame@gmail.com> wrote:
> On 16/3/16 00:12, Xidorn Quan wrote:
>>
>> On Wed, Mar 16, 2016 at 7:59 AM, Myles C. Maxfield <mmaxfield@apple.com
>> <mailto:mmaxfield@apple.com>> wrote:
>>
>>
>>     > On Mar 14, 2016, at 7:03 PM, Xidorn Quan <quanxunzhen@gmail.com
>> <mailto:quanxunzhen@gmail.com>> wrote:
>>     >
>>     > Hi,
>>     >
>>     > It seems to me that the spec is not clear about what should happen
>> if conflicting tags are specified for font-feature-settings. For example, if
>> you set "font-feature-settings: 'hwid', 'twid', 'qwid'", only one of them
>> can be chosen, but it is not clear which would win in that case.
>>
>>     Is there a repository somewhere listing every combination of
>>     conflicting font features?
>>
>>
>> I believe at least most of variants conflict with each other. Not sure
>> about other features.
>>
>
> IMO, this is out of scope for CSS-Fonts. The font-feature-settings property
> simply specifies some OpenType feature tags to be set.
>
> What happens from there on -- and in particular, how "competing" features
> interact -- is a matter for the OpenType spec,[1] and in most cases (except
> where script-specific shaping specifications mandate a particular order of
> feature application) it's the font designer who determines the interaction
> or relative priority of the features, based on the ordering of lookups
> within the font.
>
> So for example, if the style calls for
>
>   font-feature-settings: 'hwid', 'twid', 'qwid';
>
> all of these feature tags will be set; which glyphs will actually result is
> dependent on how the font designer orders the relevant lookups within the
> font.

Strongly agree.  Authors shouldn't probably *shouldn't* set
conflicting things, but there's nothing inconsistent or undefined
about doing so.  Nothing needs to be done on our end.

~TJ

Received on Wednesday, 16 March 2016 17:11:32 UTC