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Re: [css3-fonts] alternative to font-size-adjust:auto [was Re: Agenda conf call 21-aug-2013]

From: John Daggett <jdaggett@mozilla.com>
Date: Tue, 27 Aug 2013 18:28:39 -0700 (PDT)
To: Vladimir Levantovsky <Vladimir.Levantovsky@monotype.com>
Cc: www-style@w3.org
Message-ID: <398618007.5478536.1377653319831.JavaMail.zimbra@mozilla.com>

Hi Vlad,

> No, I am not arguing for changing the way how 'em' unit value is
> calculated. Considering that the stated goal of 'font-size-adjust'
> is maintaining a relative height of the lowercase characters to
> improve legibility - this adjustment should not change the line
> spacing. I was simply saying that the details of the scaling
> behavior and the relationships between font-size, font-size-adjust
> and line-height (everything that we just discussed) aren't stated in
> the spec (or it may be mentioned elsewhere but referenced in the
> CSS3 Font Module) - I think it should be.

The 'line-height' property isn't defined in the Fonts spec nor do I
think that's the best place for it.  So I think the best way to deal
with your concerns is to add a note warning authors of the possible
interactions of 'font-size-adjust' and 'line-height'.  I've updated the
spec with the note below:

http://dev.w3.org/csswg/css-fonts/#font-size-adjust-prop

# In CSS, authors typically specify ‘line-height’ using ‘em’ units so
# that the ‘line-height’ is linked to the font size. Since the
# ‘font-size-adjust’ property affects the font size used but does not
# affect the size of font relative units, authors should take care
# setting the line height when ‘font-size-adjust’ is used. Setting the
# line height too tightly could result in overlapping lines of text in
# this situation. 

> I am not arguing for the existing behavior to change but I do want
> to see it defined somewhere - both for implementers and for authors.
> Adding an informative note for authors would be fine but I think
> that the definition of the relationship between font-size,
> font-size-adjust and line-height should be normative.

As I mentioned previously, the linkage between 'line-height' and
'font-size' is via font relative units.  This is defined normatively,
both in CSS 2.1 and CSS3 Values.  CSS3 Fonts should only define
normative behavior for 'font-size-adjust' and its effect on font
relative units.

Cheers,

John Daggett
Received on Wednesday, 28 August 2013 01:29:07 UTC

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