W3C home > Mailing lists > Public > www-style@w3.org > August 2013

Re: [css3-fonts] font-size-adjust auto issue

From: John Daggett <jdaggett@mozilla.com>
Date: Wed, 21 Aug 2013 06:36:25 -0700 (PDT)
To: www-style@gtalbot.org
Cc: Vladimir Levantovsky <vladimir.levantovsky@monotype.com>, W3C Style <www-style@w3.org>
Message-ID: <1515229488.4363162.1377092185477.JavaMail.zimbra@mozilla.com>

GĂ©rard Talbot wrote:

> I think I understand what Vladimir wanted to say. Generally
> speaking, most of the time, the 'auto' keyword refers to default
> value, the per se value or initial value. Not in this case. And so,
> the use of auto is a bit counter-intuitive from a CSS perspective.
> 
> body
> {
> font-family: "Times New Roman";
> font-size-adjust: auto;
> }
> 
> really does nothing. If "Times New Roman" is an available and
> installed font, then 'font-size-adjust: auto;' does nothing,
> accomplishes nothing. 

It's hard to know what "does nothing" here means.  The 'auto' value
means use the aspect value of the *default font*.  If that's
Liberation Sans for your browser, then whether it "does nothing" or
not depends upon whether the aspect value of Times New Roman is
different or not.  If it is, then this *will* do something.

In this case:

  a  = aspect value of default font (e.g. Liberation Sans)
  a' = aspect value of Times New Roman

> Let's take your example here:
> 
>    font-family: Futura, Verdana;
>    font-size-adjust: auto;
>    font-size: 20px;
> 
> I do not have Futura font installed on my Linux (debian-based) system. I
> do not have Verdana installed either.

In this situation, no change will occur.  If neither Futura or Verdana
is available, then the default font will be used.  Hence both (a) and
(a') will be the same, they will both be the aspect value of the
default font.

> The only way I can see this 'auto' value working would be if the
> user agent has a list (or map) of font names with correspondent
> aspect value, especially font names of fonts that are not installed
> on the user's operating system.

No, 'auto' simply sets the font-size-adjust value to the aspect value
of the default font.  An author tunes the font size to what they want
with the set of fonts they have, then let's font-size-adjust assure
that in situations where fallback fonts are used instead that the text
has roughly the same readability.

> ~$ fc-match Futura
> DejaVuSans.ttf: "DejaVu Sans" "Book"
> 
> So, my system will resort to "DejaVu Sans" font instead which has an
> aspect value of 0.55. In such situation, what would be the value of a
> variable in the c  =  ( a / a' ) s equation ?

Precisely as noted above, both (a) and (a') would be 0.55 and no size
adjustment would occur.

Cheers,

John Daggett
Received on Wednesday, 21 August 2013 13:36:52 UTC

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