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RE: ems versus pixels

From: Rowan Smith <rowan@absolutely.co.nz>
Date: Wed, 2 Jan 2002 10:41:41 +1300
To: "Charles McCathieNevile" <charles@w3.org>
Cc: <w3c-wai-gl@w3.org>
Message-ID: <IMEDJHJFHLCBOPPFCIBEMEOACHAA.rowan@absolutely.co.nz>
Hi Charles

I'm using layers as a means of positioning blocks that make up elements of a
page (which contain text), rather than as a means of controlling the text
directly. Changes to text size etc should still fit within the blocks. The
page in question degrades logically in the absence of styles, so I guess my
question was about maintaining the visual integrity (ie layout) of an
accessible page.

Given that my (intended) use of px was to preserve visual appearance, I was
wondering if that got in the way of users who don't rely on the visual but I
can't think why it should.

-----Original Message-----
From: Charles McCathieNevile [mailto:charles@w3.org]
Sent: Wednesday, 2 January 2002 2:46 a.m.
To: Rowan Smith
Cc: w3c-wai-gl@w3.org
Subject: Re: ems versus pixels

Well, the accessibility downside depends on what you are soing with your
layers. If you are going to have text positioning determined by them, and
people changing text sizes or window sizes to suit their needs is going to
make a big mess, then the accessibility downside is that the design (not
using pixels, which is really a fairly small part) isn't going to work. In
this case I would suggest changing the design to start with, to one where it
does work to specify sizes in em units.

If you are trying to put a pretty border around the edge of a page, or place
a picture that doesn't scale properly anyway, then there is probably no real
problem that could be solved by switching to em units.

As I undertstand it the techniques document, where you have obviously
is a FAQ, and raising further issues on it means that there is a need for
some more material there.



On Tue, 1 Jan 2002, Rowan Smith wrote:

  Hi there

  WAI Priority 3 guidelines (WCAG Checkpoint 3.4) recommend using relative
  units rather than absolute. The Techniques document suggests that using
  rather than pixels as a unit is a way of doing this even when using

  OK, I can understand that for text specifications like font sizes and line
  heights, but does it apply to positioning layers on a page using CSS? Is
  there an accessibility downside of positioning layers (div tags) by using



Charles McCathieNevile    http://www.w3.org/People/Charles  phone: +61 409
134 136
W3C Web Accessibility Initiative     http://www.w3.org/WAI    fax: +1 617
258 5999
Location: 21 Mitchell street FOOTSCRAY Vic 3011, Australia
(or W3C INRIA, Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex,
Received on Tuesday, 1 January 2002 16:42:34 UTC

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