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Official lines Re: Using em or percent for properties that need to change

From: Charles McCathieNevile <charles@sidar.org>
Date: Tue, 17 Aug 2004 19:38:35 +0300
To: "Andy Budd" <andy@message.uk.com>, W <w3c-wai-ig@w3.org>
Message-ID: <opscv0mlzbw5l938@widsith.local>

On Tue, 17 Aug 2004 16:57:40 +0100, Andy Budd <andy@message.uk.com> wrote:

> I've discussed this issue on various accessibility, usability and web  
> design forums/mailing lists and all I get is personal bias. What I'm  
> interested in is hearing what the official WAI line is.

Then you are on the wrong list. There is one place where WAI makes  
decisions like this, the WCAG working group. (Although the Protocols and  
Formats group smetimes works with them where there is overlap in scope,  
this doesn't seem to be such a case).

Since the original checkpoiint on using relative units was written into  
the WCAG 1 recommendation, the group has made one revision, which was to  
clarify that for images and margins, there might be good reasons for  
sticking with other units as an erratum [1]. I would hope people are  
familiar with that, but wouldn't bet on it.

As the person who (believes he [2]) proposed the checkpoint in the first  
place, it was intended to preclude things like a layout fixed in pixels  
with the font in em units. There has been a fair bit of discussion about  
this over the years, and I am not sure if there is a current consensus in  
the WCAG group. That is effectively what you have to have to claim there  
is an official WAI line on this.

I interpret it as Tina, John and Patrick have suggested. The argument that  
convinces me of the need for fluid layouts is the wide range of  actual  
screen sizes, which includes window sizes.

I am familiar with users either squeezing everything into a small space to  
cope with things like tunnel vision, expainding the page to take up lots  
of space, so I can scan as much as possible of the structure while  
maintaining the text at a readable size (my personal requirements - based  
on relatively minor vision impairment and extremely inor motor  
impairments), expanding the text to a very large size (2 x 5 characters on  
the screen) through a wide variety of magnification mechanisms (seems all  
have some problems and some benefits).

For what it is worth I include below what the EuroAccessibility group  
agreed to on the matter:

Note their view on px...

3.4 Use relative rather than absolute units in markup language attribute  
values and style sheet property values. [Priority 2]
Zeist Face-To-Face Meeting
For any font styling or layout sizing don't use absolute units (px, pt,  
pc, in, cm).
Are images in raster or vector formats.
Check in the page?
Check in the linked style-sheet?

London Face-To-Face Meeting - Additions and amendments to the work done in  
Zeist Face-To-Face Meeting.

Technology Specific Questions
Have they used absolute units to size scalable elements.
Have they used absolute units to position elements.
]]] -  

There is also some discussion along the lines of the WCAG erratum [2] -  
check around  

To sum up:

I think there have been arguments based on accessibility that have been  
produced in your discussions - but it is sometimes easy to miss that they  
are not just a "personal bias" but one which is based on an identifiable  
accessibility need (albeit one that is too often left unexplained in the  
discussion :-(

This is a place to sound out a community of interested people - the WCAG  
group is where you get the official WAI line on WCAG.

Constructive participation in that group, detailed suggestions for  
improvement to their work, are always welcome. Baseless mudslinging is  
something they get too. On good days they can read into it whatever real  
point there might have been, but as far as I can tell it isn't generally  
the most effective way to get the group to see their way to solving  
problems with the guidelines.


Charles McCathieNevile

[1] http://www.w3.org/WAI/GL/WAI-WEBCONTENT-ERRATA#entry-5
[2] I had a a brief look and found  
http://lists.w3.org/Archives/Public/w3c-wai-gl/1998AprJun/0251.html which  
seemed to be the first time the suggestion was made, plus an assertion  
that I wrote what amounts to the current checkpoint made a few months  
later when it was shiny and new -  
http://lists.w3.org/Archives/Public/w3c-wai-gl/1998JulSep/0092 is the end  
of that thread. I don't think I did a great job on the checkpoint, but I  
think I have explained what I meant in a way that has been very consistent  
over the subsequent 6 years.

Charles McCathieNevile         charles@sidar.org
FundaciĆ³n Sidar             http://www.sidar.org

NB: Once upon a time I worked for WAI. Before that I worked for a  
University in Melbourne, and participated in WAI as a W3C Member  
representative. Currently I do neither. Although on specific occasions I  
will pass the agreed views of Sidar's WCAG 2 review group, normally to the  
WCAG working group, this is my personal opinion and I haven't asked, so  
don't know, if anyone in Sidar would endorse it. Let alone anyone else...
Received on Tuesday, 17 August 2004 17:39:11 UTC

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