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RE: Technique 3.4.1 Check document for relative units of measure

From: Michael Cooper <mcooper@cast.org>
Date: Mon, 2 Oct 2000 10:00:16 -0400
To: "WAI ER IG List" <w3c-wai-er-ig@w3.org>
Message-ID: <NCBBJOMIELMIDGCAPFCIMEJJDIAA.mcooper@cast.org>
I think the problem is that the HTML spec does not define relative units for
table borders. The "em" unit does not exist anywhere at all in HTML - only
in CSS. The only measurement units available in HTML are pixel sizes,
percent sizes, and a number from 0 to 7 to represent font size. Of those,
the table border attribute only accepts the pixel size. I'm surprised
browsers were able to do anything with an unrecognized attribute value type,
but am not surprised that they pretend it's a pixel measurement.

What I've begun experimenting with is I'll use a pixel measurement for a
table's border attribute, one that seems like it will work in most
situations, for backward compatibility. Then I also apply a stylesheet that
uses a relative measurement, such as an em. That trick has worked in Opera
and I think IE but not in Netscape. By worked, I mean, if I scale up the
font size, the border thickness scales too.

Michael

-----Original Message-----
From: w3c-wai-er-ig-request@w3.org
[mailto:w3c-wai-er-ig-request@w3.org]On Behalf Of Chris Ridpath
Sent: Thursday, September 28, 2000 11:48 AM
To: Charles McCathieNevile
Cc: WAI ER IG List
Subject: Re: Technique 3.4.1 Check document for relative units of
measure


I just tried a test table with Netscape 4.7 and IE5. Both browsers exhibit
the same behaviour.

Any table border size 1em or less shows up the same as a 1 pixel border,
independent of the document font size.
A table border of 2em displays the same as a 2 pixel border, independent of
the document font size.
A table border of 3em displays the same as a 3 pixel border, independent of
the document font size.

So it appears that the browsers ignore the relative 'em' size and convert
the border to an absolute number.

Chris

----- Original Message -----
From: "Charles McCathieNevile" <charles@w3.org>
To: "Chris Ridpath" <chris.ridpath@utoronto.ca>
Cc: "WAI ER IG List" <w3c-wai-er-ig@w3.org>
Sent: Friday, September 22, 2000 9:15 AM
Subject: Re: Technique 3.4.1 Check document for relative units of measure


> .1 em is a good size. For someone who is using a very large fot so they
can
> see it, a 2px border may just disappear, but a .1 em border will still be
> visible.
>
> Charles McCN
>
> On Wed, 20 Sep 2000, Chris Ridpath wrote:
>
>   Could the 'border' attribute be an exception to this rule? It's a common
>   practice to use 1 or 2 for a table/image/frame border to indicate that
there
>   should be some sort of thin line surrounding the object. If we do
require a
>   relative measure for a border, what would it be? (I think that an 'em'
or
>   'ex' would be too large to replace a 1 pixel border.)
>
>   Chris
>
>
>
> --
> Charles McCathieNevile    mailto:charles@w3.org    phone: +61 (0) 409 134
136
> W3C Web Accessibility Initiative
http://www.w3.org/WAI
> Location: I-cubed, 110 Victoria Street, Carlton VIC 3053, Australia
> September - November 2000:
> W3C INRIA, 2004 Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex,
France
>
Received on Monday, 2 October 2000 10:06:19 UTC

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