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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: Wed, 21 Aug 2013 23:14:25 -0700 (PDT)
To: Jonathan Kew <jfkthame@googlemail.com>
Cc: www-style@w3.org
Message-ID: <467516312.4504808.1377152065974.JavaMail.zimbra@mozilla.com>

Jonathan Kew wrote:

>> The LC period for Fonts runs through tomorrow.  Right now there's
>> an open issue regarding 'font-size-adjust: auto' that I think needs
>> to be addressed before we can move to CR.  I'm hoping we can wrap
>> this issue up this week which will allow us to resolve to move to
>> CR on next week's call.
> It seems to me from the recent thread here that the biggest problem
> with font-size-adjust:auto is that people are misunderstanding what
> it means. Even experienced spec-readers here seem to easily misread
> # Behaves just like <number>, except the number used is the aspect
> # value calculated by user agents for the first font in the list of
> # fonts defined for the initial value of the ‘font-family’ property.
> as though it said
> # Behaves just like <number>, except the number used is the aspect
> # value calculated by user agents for the first font in the list of
> # fonts in the ‘font-family’ property.
> (and then start to wonder what happens if that "first font" isn't
> available, etc.) Not sure how to make that clearer, but I think
> we've seen ample evidence that the current text is not communicating
> adequately.

I agree, it seems to me most of the problem here is confusion over the
precise nature of the intended behavior.  I think the spec is clear but
it would definitely benefit from a note explaining why the "initial value
of 'font-family'" is not equivalent to the first font in the font list.

> In addition, there's the question of whether "auto" is a good name
> for this behavior.

I think the goal of this value is simply to fix the aspect value to a
constant value.  This allows an author to lay out text on a page
knowing that the user will see text with roughly the same x-height
independent of fonts available.  So I think "auto" is perfectly
reasonable here.

> Here's a thought: suppose that instead of "auto", you could say
>    font-size-adjust: <generic-family>;
> to specify that the UA uses its calculated aspect value for the font
> that corresponds to the given CSS generic. So typical usage might be
>    font-family: Gentium, Times, Georgia, Liberation Serif, serif;
>    font-size-adjust: serif;
> would match whichever of the serif fonts is used to the browser's
> default serif face...

So the idea is that there are different values for each generic type?
I'm not sure this behavior would be any better than the functionality
of the existing 'auto' value.  I think it would be harder for authors
to understand; where 'auto' to some extent implies that the user agent
is trying to use good default behavior, using generics means the
author would need to understand the difference between
'font-size-adjust: serif' and 'font-size-adjust: sans-serif'.
I'm not sure I see an easy rule of thumb way of deciding that.

I think we still need to hear from Vlad about this issue but at this point 
I guess I see several different options:

1) 'auto' is fine as defined but explain clearly that it doesn't imply the
   use of the aspect value of the first font in the font list

2) switch to using generics, instead of 'auto', have 'serif', 'sans-serif', etc.

3) drop the value altogther and suggest the use of an arbitrary value (e.g. 0.5)

The one advantage of (3) is that it allows authors to know absolutely
that text will *always* have the same x-height as what they see in
their design environment.  Even if the fonts are different on other
platforms, the font size will always be scaled so that the x-height of
the font used matches that of the font used by the author in their
design environment.  The use of 'auto' or generics suffers from the
problem that different user agents may have different default fonts
with varying aspect values.


John Daggett
Received on Thursday, 22 August 2013 06:14:57 UTC

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