Re: [css3-fonts] default font features

On 17/7/12 19:17, Sergey Malkin wrote:
> Rob wrote:
>> If CSS 'letter-spacing' is greater than zero, we disable
>> discretionary ligatures, because it seems safe to assume that
>> matches the author's intent. That behavior could (and I think
>> should) be written into the spec.
>
> This is exactly behavior that should not be in the spec. Why would
> you turn off discretionary ligatures, but not standard?

I think Rob's use of the term "discretionary" was unfortunate; he did 
not mean "discretionary ligatures" as typically found in the 'dlig' 
feature, but rather all ligatures except those that are linguistically 
required - in other words, in OpenType terms we turn off 'liga', but 
leave 'rlig' (for Arabic lam-alef forms) enabled.

The CSS3 Text spec for letter-spacing says that "[w]hen the resulting 
space between two characters is not the same as the default space, user 
agents should not use optional ligatures." I think "optional ligatures" 
here means ligatures such as "fi" and "fl" that are a typographic 
refinement in typical Latin fonts, as opposed to ligatures (such as 
Arabic lam-alef or Devanagari ksha) that are required for correctness in 
a given writing system.

JK