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Re: [css-text] Amending hanging-punctuation for Western typography

From: John Hudson <john@tiro.ca>
Date: Thu, 7 Apr 2016 10:46:56 -0700
To: Alan Stearns <stearns@adobe.com>, fantasai <fantasai.lists@inkedblade.net>, Jon Lee <jonlee@apple.com>, Jan Tosovsky <j.tosovsky@email.cz>
Cc: "www-style@w3.org" <www-style@w3.org>
Message-ID: <57069D10.8090705@tiro.ca>
On 06/04/16 17:22, Alan Stearns wrote:

>> Overall I think it sounds very complicated... and I'm not convinced
>> >it'll work that great in practice. Wouldn't it make more sense to
>> >be able to have a kerning value for the start/end of the line and
>> >to have a switch to just turn that on? That way the font designer
>> >can do full-on optical alignment, which is the goal in Western
>> >hanging punctuation anyway.
> No, because it depends on the character - as Jon noted. A hyphen should hang completely off the edge, while an em-dash might only hang halfway. Optical alignment takes a look at the shape of the glyph and makes individual adjustments, it doesn’t apply a single kerning value.

Point of information:

OpenType has registered GPOS features for optical margin alignment, so 
in theory a font can contain explicit information for beginning- and 
end-of-line adjustments to be made. In practice, I've never seen this 
implemented in either software or fonts, and where optical margin 
alignment or hanging punctuation is implemented it tends to be 
algorithmically without reliance on font data.

As is often the case, it is difficult to tell whether the absence of 
such data in fonts is due to lack of software support, or vice versa.

If optical margin alignment were implemented in CSS in such a way that 
browsers were to check for the presence of either/or <ltbd> Left Bounds 
and <rtbd> Right bounds layout features* in a font before falling back 
to algorithmic margin alignment, that would at least open the 
possibility to font developers to include such data in their fonts.

* I recommend ignoring the <opbd> Optical Bounds feature. The three 
features were registered by Adobe very early in the development of 
OpenType Layout, and use a speculative model in which one feature 
references two other subsidiary features. In fact, the higher level 
feature isn't required at all, and confuses font features with 
application setting or UI. It's possible for a layout engine to go from 
an application setting or markup directly to the appropriate left or 
right bounds feature without needing to reference <opbd>.



John Hudson
Tiro Typeworks Ltd    www.tiro.com
Salish Sea, BC        tiro@tiro.com

Getting Spiekermann to not like Helvetica is like training
a cat to stay out of water. But I'm impressed that people
know who to ask when they want to ask someone to not like
Helvetica. That's progress. -- David Berlow
Received on Thursday, 7 April 2016 17:48:00 UTC

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