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

From: Leonard R. Kasday <kasday@acm.org>
Date: Wed, 03 May 2000 16:27:12 -0400
Message-Id: <4.3.1.2.20000503162354.00c94780@pop3.concentric.net>
To: "Michael Cooper" <mcooper@cast.org>, <w3c-wai-gl@w3.org>
Cc: <w3c-wai-er-ig@w3.org>
I had posted this to two lists... so my reply to this didn't get over here.

So here it is again,,

Michael... thanks for that example of what to do to avoid overlapping 
text.  That's a good illustration of the point I was trying to make: that 
it isn't enough to use relative units, like EM.  More is needed.

One way to write the guidelines is to restrict use of CSS layout to those 
features that duplicate table layout... although this may well be too 
restrictive a use of CSS.

Everyone... please follow up any more discussion on this on the guidelines 
list.  I'll do the same.

Len

At 03:04 PM 5/3/00 -0400, Michael Cooper wrote:
>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)

--
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 16:26:37 GMT

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