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Re: Inconsistent treatment of "em" and "ex" unit when used to specify "font-size"

From: Brad Kemper <brad.kemper@gmail.com>
Date: Sun, 1 Nov 2009 21:03:12 -0800
Cc: W3C Style List <www-style@w3.org>, Thomas Phinney <tphinney@cal.berkeley.edu>, Philip TAYLOR <P.Taylor@rhul.ac.uk>, John Daggett <jdaggett@mozilla.com>
Message-Id: <DF2376C4-86C6-4A6D-BDA6-2604B8F1E7E4@gmail.com>
To: Bert Bos <bert@w3.org>

On Oct 30, 2009, at 7:03 AM, Bert Bos wrote:

> On that last sentence of the quoted text (which is marked as an  
> issue in
> the working draft): The WG currently believes that the text of CSS 2.1
> ("In the cases where it is impossible or impractical to determine the
> x-height, a value of 0.5em should be used.") is still the best and can
> be inserted unchanged at that point in the CSS3 module.

Should a note about this also be added to 'font-size-adjust'? [1]

That part of that module does not actually mention 'ex' units, but if  
I understand it correctly, it would need the same bit of info from the  
font, and would also need to guess at it, if it is "impossible or  
impractical to determine the x-height" by reading it directly from the  
font metrics.

Or maybe the wording of 'font-size-adjust' can be adjusted to describe  
what it is doing in terms of equalizing the 'ex' measurement of all  
the fonts in the font-family list? For instance, maybe "aspect ratio"  
can be defined as "1ex, as measured in ems" (thus, if '0.5' is the  
'aspect ratio' for a given font, then it is actually '1ex', measured  
as '0.5em'). In this case, no other explanation about the undetermined  
x-heights is needed in the fonts module, because that explanation is  
already in the "CSS Values and Units" module.

I also think that would be a bit easier to comprehend than the current  
opening explanation, which speaks of "the relative height of lowercase  
letters", and then later uses a lower case "b" as an example (which  
has an extender making it taller than 1ex).


[1] http://www.w3.org/TR/2009/WD-css3-fonts-20090618/#relative-sizing-the-font-size-adjust-pro

Received on Monday, 2 November 2009 05:03:49 GMT

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