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RE: valid mark-up only priority 2!! WAS valid comments

From: Jukka Korpela <jukka.korpela@tieke.fi>
Date: Tue, 12 Nov 2002 09:31:41 +0200
Message-ID: <621574AE86FAD3118D1D0000E22138A95BDF45@TIEKE1>
To: WAI IG <w3c-wai-ig@w3.org>

Jon Hanna wrote:

> From a perspective of accessibility only many examples of 
> invalid markup are pretty harmless,

Indeed, especially since common markup errors are things like
attempts to put block level elements inside <font> elements,
where the real problem is not formal validity.

> so it seems reasonable that it is of less priority than
> cases with clear and well demonstrated accessibility issues 

Well, I wouldn't quite agree. All this priority thing confuses me.
For example, what are the clear and well demonstrated accessibility
issues for the checkpoint "4.1 Clearly identify changes in the natural
language of a document's text and any text equivalents (e.g., captions)."?

It's fairly easy to list down issues involved _in principle_. But then
again, the same applies to invalid markup. Invalid markup means that
the document syntax does not comply with a published "grammar", and
this in turn implies that any software, such as assistive technology
or special browser, may get thoroughly confused. But on the practical side?

The guideline for using valid markup (in the sense of checkpoint 3.2,
which is actually much more than validity, since it requires the use
of a "published DTD", effectively referring to the small set of DTDs
published by the W3C) might, in rare cases, even conflict with

The WCAG 1.0 text says:
"Content developers may be tempted to use (or misuse) constructs that
achieve a desired formatting effect on older browsers. They must be aware
that these practices cause accessibility problems and must consider whether
the formatting effect is so critical as to warrant making the document
inaccessible to some users."
Fair point, but consider the possibility of using constructs that
achieve _accessibility improvements_ on _newer_ browsers but haven't
been canonicalized into a W3C-approved DTD.

Browser vendors haven't been that eager to implement accessibility
enhancements that are not present in published DTDs, but they just might. At
least some "minority" browser vendors.

Or to take a specialized, yet real, example: Suppose your document contains
the string "-42". It is known that the most widely used browser treats this
as splittable*), in the sense that it may put "-" at the end of a line and
"42" at the start of the next one. This may confuse any user, and especially
users with cognitive disabilities. As far as I know, the only effective
weapon against that (in the general case) is to use <nobr>-42</nobr>. This
invalid markup, when used in cases like this, causes no known problem, to
accessibility or otherwise. I'm not saying it _should_ be used; just that
there are good arguments in favor of using it - for accessibility too.
*) For the boring details, consult

In most cases, of course, there's no good excuse for using invalid markup,
unless you count relative lack of time and other resources to fix past
errors. ("Relative lack" refers to the possibility that there might be
other, more urgent problems to fix.)

There's a particular reason to avoid emphasizing the importance of validity
too much in the accessibility context. It seems that surprisingly often
validity is presented as something that somehow guarantees interoperability
and even accessibility. Does the following sound familiar?
"To show your readers that you have taken the care to create an
interoperable Web page, you may display this icon on any page that

Jukka Korpela, senior adviser 
TIEKE Finnish Information Society Development Centre
Diffuse Business Guide to Web Accessibility and Design for All:
Received on Tuesday, 12 November 2002 02:32:18 UTC

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