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Re: Guideline 3.4 comment (ralative vs. absolute units)

From: Charles McCathieNevile <charles@w3.org>
Date: Mon, 10 Dec 2001 16:02:33 -0500 (EST)
To: Vadim Plessky <lucy-ples@mtu-net.ru>
cc: <w3c-wai-gl@w3.org>, <wai-wcag-editor@w3.org>
Message-ID: <Pine.LNX.4.30.0112101547490.21737-100000@tux.w3.org>
Hi Vadim,

in the errata page for WCAG as of today (11 december 2001 0750UTC+1100) there
is an error recorded as number 5, added november 1999, which suggests:

  ...If absolute units are used, validate that the rendered content is
  usable... For example, do not proportionally size raster images.

I think the point is that relative units should be used for font sizes, and I
would argue that it is appropriate to use them for layout as well -
especially for layout of text.

In general I think em and % are better than "big, bigger, small" etc because
the size differences in the recommendation are too extreme and the
implementation is very varied. And I think they are the only way to get font
sizes "right" because I find it very difficult to read what some content
developers obviously thinks is the appropriate font size.

(more detailed comments/responses below)

cheers

Charles

On Mon, 10 Dec 2001, Vadim Plessky wrote:

  Hello,

  I have a comment on guideline 3.4 of WCAG 1.0
  http://www.w3.org/TR/WAI-WEBCONTENT/#gl-structure-presentation
[snip]
  IMO this is really wrong.
  You can design web page which doesn't use text at all (pure
  formatting/presentation purpose), like:

  <html>
  <style type="text/css">
    div { border: 10pt solid blue; background: silver;
           width: 100pt; height: 80pt }
  </style>
  <div></div>
  <body>

  Using 'em' for defining width/height iof DIV element here is really NONSENSE
  - as *there is no font used in that page at all*.
  Besides, you can't use percentage here - as you never know what is the
  browser's screen width (especially if you you XHTML basic - as <script> is
  not supported in XHTML basic, you can't get screen.width and screen.height.

Actually I am not sure why you think it is nonsense to use em or % - it seems
to me that both of those would work, although I ma not sure of the effect you
are trying to create.

  If there was something wrong in using 'pt' or 'cm' in CSS definitions - than
  'pt' and 'cm' could be just excluded from CSS specifications. As they are
  present in CSS1/CSS2 - there is nothing wrong in using them.

That logic doesn't hold up unless we claim to be perfect in all our
specifications. For that matter, the order of the Cascade in CSS2 is vvery
different from that in CSS1 because we felt that in CSS1 it was wrong, but we
only make improvements after we know of the problem, and it is difficult to
update a Recommendation.

  Besides, using 'pt' (instead of 'px') is the only way to get font size
  *right* - and current CSS specification *doesn't recommend* using 'smaller'
  or 'bigger' - as these properties are device-dependant, so using them you
  limit your page portability and possibility to view it on different kind of
  devices.
Received on Monday, 10 December 2001 16:02:36 GMT

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