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RE: Low Vision and CSS (The EM is not enough)

From: Michael Cooper <mcooper@cast.org>
Date: Wed, 3 May 2000 15:04:43 -0400
To: "Leonard R. Kasday" <kasday@acm.org>, <w3c-wai-gl@w3.org>
Cc: <w3c-wai-er-ig@w3.org>
Message-ID: <NCBBJOMIELMIDGCAPFCIMEKDDCAA.mcooper@cast.org>
The issue there is that the second paragraph on the page is absolutely
positioned with respect to the _page_, not to the paragraph above it. When a
font size change or window resize cause the first paragraph to have more
lines than you planned on, the format breaks. It's not the relative units at
issue though, it's what they're relative to. That's a subtle and
hard-to-explain distinction that I also have run afoul of, but there are
ways to make it work. In the case of this example, you can use _relative_
positioning and used em or ex units, and it would stay in the same relative
position regardless of font or window changes. For instance, try replacing
the existing style attribute with the following one:
style="position:relative; left:0em; top:2ex;".

Michael Cooper
mcooper@cast.org

-----Original Message-----
From: w3c-wai-er-ig-request@w3.org [mailto:w3c-wai-er-ig-request@w3.org]On
Behalf Of Leonard R. Kasday
Sent: Wednesday, May 03, 2000 2:04 PM
To: w3c-wai-gl@w3.org
Cc: w3c-wai-er-ig@w3.org
Subject: Low Vision and CSS (The EM is not enough)

To WCAG
Copied to ER

People with low vision often increase the default font size.  One might
think this could be accommodated by using em units instead of absolute
units, but that doesn't appear to be the case.  If you look at

http://astro.temple.edu/~kasday/wai/css-em.html

using Internet Explorer 5, with medium font size, and a window
approximately a screen width, you'll see a paragraph at the top and text
below it.  The lower text is positioned with respect to the window with
ems.  However, if you now make the window smaller, you'll see the text in
the top paragraph wrap, causing the number of lines to increase and it will
eventually overlap the text below it.

Similarly, if you make the font bigger using View->font size, you'll again
get the overlap.

The moral is that, checkpoint 3.4 to use relative units such as the EM is
not enough.  There needs to be a more general guideline that pages shall
read sensibly when default font is made larger.

For convenience, I've included the text of the referenced example in this
email.

Len

p.s.
Presently, this example works only in MSIE 5, not Opera 3.62 or Netscape
4.7.  I think MSIE is doing it right.  CSS gurus please check...

==========

This shows that text can overlap even when using ems. If you make screen
narrower or font larger the text will overlap... at least in Microsoft
Internet Explorer 5.0 (Overlap does not occur in Opera 3.62, and Netscape
Communicator doesn't show it at all).
This sentence starts out below the first one.

Len Kasday, kasday@acm.org, Pennsylvania's Initiative on Assistive
Technology, a program of the Institute on Disabilities/UAP at Temple
University
--
Leonard R. Kasday, Ph.D.
Institute on Disabilities/UAP, and
Department of Electrical Engineering
Temple University
423 Ritter Annex, Philadelphia, PA 19122

kasday@acm.org
http://astro.temple.edu/~kasday

(215) 204-2247 (voice)
(800) 750-7428 (TTY)
Received on Wednesday, 3 May 2000 15:12:35 GMT

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