Re: [css3-fonts] comments on ED of 24 May 2013

On 28/5/13 18:01, John Daggett wrote:
>
> Jonathan Kew wrote:
>

re §6.12:

>> # This means that explicitly disabling the kern feature will not
>> # affect the application of kerning data found in the ‘kern’ table
>> # (as opposed to kerning data associated with the kern feature in
>> # the ‘GPOS’ table).
>>
>> This sounds like it was describing a now-obsolete state of the
>> implementation in Firefox. For UAs that rely on HarfBuzz for text
>> shaping, this is not currently true: if the UA asks HarfBuzz to
>> disable the kern feature, this will disable *both* the kern feature
>> in the ‘GPOS’ table *and* the application of the ‘kern’ table data.
>>
>> The connection between ‘GPOS’ and ‘kern’ table kerning is a
>> low-level implementation detail; I'm not sure CSS Fonts needs to
>> deal with this, but the current text does not describe what actually
>> happens - at least for Gecko, but likely for other UAs as well if
>> they use the HarfBuzz shaping engine.
>
> While the 'font-kerning' property defines behavior that covers
> old-style kerning data (i.e. the 'kern' table), I explicitly
> did not extend the same behavior to 'font-feature-settings: "kern" on'.
> The 'font-feature-settings' property is a low-level way of passing
> down specific OpenType parameter settings, so defining "extra"
> behavior like this is sort of odd.
>
> I guess making an exception in this one case is okay but I definitely
> think CSS should *not* be extending the meaning of specific features
> by adding behavior to them ("let's have feature xxx mean .... when
> conditions yyy and zzz are true").
>

It looks like the current (19 August 2013) text here is unchanged, which 
means Gecko (and likely any other harfbuzz-based engine) will be 
non-compliant with this section. Were you going to include some kind of 
exception to reflect the real-world behavior we have here, or are you 
expecting the implementation to change?

JK

Received on Thursday, 22 August 2013 23:38:29 UTC