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Re: Clarification on normative glossary definition of "Large scale (text)"

From: CAE-Vanderhe <gregg@raisingthefloor.org>
Date: Tue, 7 Oct 2014 10:28:52 -0500
Cc: IG - WAI Interest Group List list <w3c-wai-ig@w3.org>
Message-Id: <D0CEF615-8AF7-49A6-8838-1C6F63E7D114@cae.wisc.edu>
To: "Patrick H. Lauke" <redux@splintered.co.uk>
> So basically, the 18point/14point values are anchored on the assumption that 1em is set to the default UA text size *and* is readable.

GV:  No.  Hmmm  let me try again.    18/14  point values are based on the fact that the user has a screen/resolution/zoom/viewing distance that makes 1em readable.   

Those point sizes are ONLY used in WCAG to determine when contrast can be reduced.   The assumption is that the text is readable at normal size (due to  the screen/resolution/zoom/viewing distance that the user has set)  and this is just saying that text that is LARGER can have a lower contrast.

> 
> If an author set the base font size on HTML/BODY to be something far too small, like 0.5em, would text which is then later defined to be 1.5em still count as large scale, as it is large relative to the base font size? So "large text" would simply mean "larger by at least a factor of 1.5 compared to the base font"? If so, this part is confusing

GV:  Yes.  it is easier to understand if you remember that this is just used for contrast determination.  it has nothing to do with the readability of the standard sized font on the page. 

> 
> "The point size should be obtained from the user agent, or calculated based on font metrics as the user agent does, when evaluating this success criterion."
> 
> as in the scenario above, the calculated pt size would end up being 9pt, *but* it would still be 1.5x the size of the base font.
> 
> In short, are the values of 18pt/14pt anchored to the CSS pixel size (regardless of whether it's actually close to the reference pixel dimensions or not, leaving out any issues of viewport), or are they used as an indication of relative size, in which case it would be more appropriate to basically say that ("text that is 1.5x the size of the base font size, or 1.2x the size and bold”).

GV:  Again. see above.       WCAG doesn’t talk about font size and readability because the size of the font to the viewer is not under the control of the author.  They can change RELATIVE size but the user can change that with the screen/resolution/zoom/viewing distance.     And it is assumed that the viewer will use a screen/resolution/zoom/viewing distance  that works for them for the web.

It is clearly not best practice to set your overall web page font size to be .5 em.    But there is nothing in WCAG to prevent it — since even setting it to 1.5 em would not help someone viewing it with a high pixel density - without changing the screen/resolution/zoom/viewing distance.  

Does that help?

G


> 
> P
> -- 



On Oct 7, 2014, at 2:51 AM, Patrick H. Lauke <redux@splintered.co.uk> wrote:

> On 07/10/2014 03:48, CAE-Vanderhe wrote:
>> The WCAG definition covers the issues quite well.  The issues raised
>> in these various posts was considered in creating the SC and the
>> definitions.
>> 
>> The goal is to have text be larger than typical font.    The size
>> that a font appears to the user is dependent on lots of things - like
>> zoom of browser, pixel density of the display, scaling (some displays
>> like the retina) do not render a pixel as one pixel on the display,
>> viewing distance, etc — all of which are outside of the control of
>> the author — so it is meaningless to have an accessibility guideline
>> for web authors that requires that the user see the font in a
>> particular size, or angle subtended.
>> 
>> So the guidelines were written to talk about minimum RELATIVE size of
>> the font.   If the font is relatively larger — and the user does not
>> use a screen resolution that is too dense — it all works out.
> 
> So basically, the 18point/14point values are anchored on the assumption that 1em is set to the default UA text size *and* is readable.
> 
> If an author set the base font size on HTML/BODY to be something far too small, like 0.5em, would text which is then later defined to be 1.5em still count as large scale, as it is large relative to the base font size? So "large text" would simply mean "larger by at least a factor of 1.5 compared to the base font"? If so, this part is confusing
> 
> "The point size should be obtained from the user agent, or calculated based on font metrics as the user agent does, when evaluating this success criterion."
> 
> as in the scenario above, the calculated pt size would end up being 9pt, *but* it would still be 1.5x the size of the base font.
> 
> In short, are the values of 18pt/14pt anchored to the CSS pixel size (regardless of whether it's actually close to the reference pixel dimensions or not, leaving out any issues of viewport), or are they used as an indication of relative size, in which case it would be more appropriate to basically say that ("text that is 1.5x the size of the base font size, or 1.2x the size and bold").
> 
> P
> -- 
> Patrick H. Lauke
> 
> www.splintered.co.uk | https://github.com/patrickhlauke
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Received on Tuesday, 7 October 2014 15:29:20 UTC

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