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RE: Some words about the terms "relative" and "absolute".

From: Gregg Vanderheiden <gv@trace.wisc.edu>
Date: Thu, 1 Jun 2006 12:25:28 -0500
To: "'Marco Bertoni'" <mbertoni@webaccessibile.org>, <w3c-wai-gl@w3.org>
Message-ID: <00af01c685a0$614aee40$8b17a8c0@NC6000BAK>

Hi Marco,

Most advisory techniques have not been written yet.

You will find it listed in the Understanding WCAG 2.0 doc as a "future link"
meaning that no one has had a chance to write it up yet.  Our focus has been
to complete enough technique writeups to check our SC.  But we have many
sufficient and most all of the advisory techniques yet to write up. 

Does that help?

By the way - anyone who want to take a stab at writing up any technique (or
submitting a new one) can just go to 
http://www.w3.org/WAI/GL/WCAG20/TECHS-SUBMIT/
and write one. 



RE: The rest of your comments
I think that the rest of your comments are quite interesting.  I don't want
to lose them.  I would suggest you wait for another few days to see if
anyone provides any input on this list -- and then reformulate them and put
them as a Public Comment on the WCAG 2.0 draft.   We can then have them in
our database when we collect all the comments on this and work it out. 


Gregg

 -- ------------------------------ 
Gregg C Vanderheiden Ph.D. 
Professor - Ind. Engr. & BioMed Engr.
Director - Trace R & D Center 
University of Wisconsin-Madison 
The Player for my DSS sound file is at http://tinyurl.com/dho6b 
 

> -----Original Message-----
> From: w3c-wai-gl-request@w3.org 
> [mailto:w3c-wai-gl-request@w3.org] On Behalf Of Marco Bertoni
> Sent: Thursday, June 01, 2006 7:46 AM
> To: w3c-wai-gl@w3.org
> Subject: Some words about the terms "relative" and "absolute".
> 
> 
> Hi,
> last week I was filling the surveys when I encountered the 
> terms "relative" and "relative positioning" (in the Team A 
> survey if I remember well).
> I think we need some clarifications about those terms, 
> expecially when they are used regarding both font sizing 
> units and CSS positioning rules.
> 
> First off all in the "Comparison of WCAG 1.0 checkpoints to 
> WCAG 2.0" [1] appendix we can read:
> 
> In General (Priority 2):
> 3.4: Use relative rather than absolute units in markup 
> language attribute values and style sheet property values.
> 
> ...that is related to:
> 
> WCAG 2.0 Success Criteria:
> This maps to an advisory technique (Using readable fonts) for 
> Guideline 1.4.
> 
> But Guideline 1.4 refer to visual and audio contrast [2] and 
> I've not yet found, even in the "Techniques for WCAG 2.0", 
> the advisory technique mentioned (Using readable fonts). 
> Perhaps someone can help me to find what I'm searching for, 
> I'm new to the group ;).
> 
> However even in the "CSS Techniques for WCAG 2.0" draft [2], 
> in wich is correctly introduced the idea of "Using em or 
> percent for properties that need to change" instead of "Use 
> relative rather than absolute units...", when I look at the 
> corresponding guideline I see mentioned "Guideline 1.3" that 
> refer to the separation of structure and presentation.
> 
> Having said that, I must point up that using terms like 
> "relative units" or "relative positioning" maybe somehow confusing:
> 
> 1) I assume that the general accessibility principle in 
> question is that users (expecially partially sighted people) 
> must be able to enlarge fonts using their visual UA tools.
> 
> 2) Microsoft Internet Explorer 6 for Windows - and all the 
> previous versions - is not able to resize text if it is sized 
> in pixels. But pixel are relative lenght units (they are 
> relative to the viewing device resolution) [4].
> 
> 3) On the other hand there are CSS absolute-size values that 
> IE/WIN can perfectly resize: the absolute-size keywords [5].
> 
> So, IMHO it is really wrong and confusing to advise CSS 
> designers that they should use relative length units to size 
> fonts. Correctly, as I told before, CSS Techniques says: "Use 
> "em" or % for properties that need to change". But we can 
> make another stride to avoid to mention a unit identifier: 
> e.g. here in Italy, in our recent accessibility law [6], we 
> have introduced a requirement (Requirement 12) that says: 
> "The presentation and textual content of a page must be able 
> to be adapted to the dimensions of the browser window used by 
> the user, without superimposing objects present or loss of 
> information such as to render the content incomprehensible, 
> including in the case of resizing, enlargement or reduction 
> of the display area or characters in relation to the 
> predefined values of these parameters.".  In other words with 
> this approach we say that the designer must size charachters 
> with a unit (not mentioned) that guarantee the enlargement of 
> text in every UA. This is expecially useful to ensure forward 
> and backward compatibility!. We cannot forget that, at the 
> time of this writing, IE 6, with all off his bugs, cover 
> almost all the market.
> 
> Directly following that we must clarify the use of the phrase 
> "relative positioning": when a CSS designer hear that words 
> he think about a CSS rule like this: #box { position: 
> relative; } [7]. But in itself a positioning scheme isn't 
> related to accessibility. Indeed (and correct me if I'm 
> wrong) when we talk about relative positioning we are 
> thinking about a concept like "use liquid design" rather than 
> a specific CSS positioning scheme. So, IMHO again, it is 
> wrong to advise designers to use a specific positioning 
> scheme. Maybe useful instead to tell them that, for example, 
> a liquid design is more accessible than a fixed design, no 
> matter which technique they use to obtain that. Obviously we 
> must first justify this suggestion.
> 
> These terminological problems are really serious: I've hardly 
> discussed, here in Italy, with tricky designers that keep on 
> using their beloved pixels for text sizing because these are 
> relative units as checkpoint 3.4 of WCAG 1.0 suggest (no 
> matter if partially sighted people using IE6/WIN cannot resize them). 
> 
> What do you think about?
> 
> Marco Bertoni
> 
> [1] http://www.w3.org/TR/WCAG20/appendixD.html
> [2] http://www.w3.org/TR/WCAG20/guidelines.html#visual-audio-contrast
> [3] http://www.w3.org/TR/WCAG20-CSS-TECHS/#syntax-data-types
> [4] http://www.w3.org/TR/CSS21/syndata.html#length-units
> [5] http://www.w3.org/TR/CSS21/fonts.html#font-size-props
> [6] http://www.pubbliaccesso.it/normative/DM080705-A-en.htm
> [7] http://www.w3.org/TR/CSS21/visuren.html#relative-positioning
> 
> 
> 
> 
Received on Thursday, 1 June 2006 17:25:36 GMT

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