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That's not just an accessibility issue: any bug needs to be tested to ensure in has no unseen consequences.
If you stick closely to exactly the bugs in the HTML and CSS of some popular sites (like Google or Yahoo) then you have some degreee of confidence that those bugs are benign across the range of user agents that [eg Google / Yahoo] consider their market.
If you insert other untesed bugs, then the onus is on you to roll out a testing program.
For HTML validation, as le_gber mentioned, some are more important than others: missing trailing slashes in XHTML are irrelevant, but missing alt attributes or broken, mismatched or ill-formed tags can make your page inaccessible.
Unless you are confident that the specific errors you are introducing will have no impact, then you should always aim for full validation of your pages.
However, it is perfectly to have a 100% valid but totally inaccessible page, as much as it is to have an invalid page which meets most accessibility criteria. Validation is merely another tool which will help you ensure the quality and accessibility of your site.
Guideline 3. Use markup and style sheets and do so properly.
[w3.org...]
If a site is using markup and it is broken, does that not break the accessibility/usability chain?
What HTML/XHTML errors can you find that can be ignored and not have an impact on the A/U of the site?
if you fail [validation] for failling to add the / at the end of one <br /> in xhtml - the site will still be accessible.
Disagree. :)
In IE, yes. Opera and FF would abort parsing and throw an error since your XML markup is broken.
While I don't think that the three -- accessibility, usability, and validation -- are synonymous of one another (you can have one without necessarily having the other), I think they are definitely related and augment the benefits. It is much easier to maintain one (refering to accessibility, usability, or validity) if you are concerned about the other two.
(...) failling to add the / at the end of one <br /> in xhtml - the site will still be accessible.
(...)In IE, yes. Opera and FF would abort parsing and throw an error since your XML markup is broken.
If we are talking about XHTML as XML, then I would argue that accessibility is already severely compromised as the medium is inappropriate for the message - ultra-strict X(HT)ML is too limiting in terms of error-handling. If we are talking about XHTML syntax served as HTML (the overwhelming majority of XHTML content) then the presence of absence of trailing slashes has no influence whatsoever on accessibility. It does however affect validity.
Same goes for other "errors" such as uppercase tags in a declared XHTML document, pages with missing or ill-formed doctypes (to the extent that the absence of a doctype does not affect page rendering), the occasional missing end tag such as
</p>. However, unless you are certain, why take the risk? Markup validated to a recognized, recent standard such as HTML 4.01 or XHTML 1.0 has the best chances of lacking parsing errors which might degrade the accessibility of the document.
3.2 Create documents that validate to published formal grammars. [Priority 2]Validating to a published formal grammar and declaring that validation at the beginning of a document lets the user know that the structure of the document is sound. It also lets the user agent know where to look for semantics if it needs to. The W3C Validation Service validates documents against a whole list of published grammars.
You won't be able to move to Priority 2 Checkpoints without validating to a DTD.
HTML Techniques for Web Content Accessibility Guidelines 1.0
[w3.org...]
1.1.4 The!DOCTYPE statement
[w3.org...]
Accessibility, Usability and Validation: Are they synonymous of one another?Can you have an accessible and usable website without HTML and CSS validation?
Accessibility, Usability and Validation: Are they synonymous of one another?
They are not synonymous [having the same or a similar meaning] else we would not be using three when any one would do. They are, however, compatible [able to exist and perform in harmonious or agreeable combination].
Accessibility: being at hand when needed.
Usability: being fit for use; being convenient to use.
Validation: testing the truth (valid proof) of something.
I visualise the three as a dynamic Venn diagram sliding together or apart depending on site requirements, budget, and time. Given both individual and technical variants I am unable to imagine a total overlap of any two, let alone all three.
* Is a w3c valid site necessarily easy (fit/convenient) to use?
* As noted by pageoneresults some (and there are several models) accessibility guidelines require grammar validation but it remains but one requirement among many. What combination of validations is valid?
* Is a site that is easy to use for me easy for you, or vice versa?
* Is a site that is easy to use necessarily valid?
* Is a site that is 'at hand' necessarily easy to use? or valid?
And then there is the quality of available tools. The major browsers for the not-so-seriously-handicapped-majority are unable/unwilling to render similar results. Imagine the lack of support and capability variance among the various browsers for the more-seriously-handicapped-minority.
These are not reasons to ignore validation, usability, or accessibility. Nor reasons to address only their 'similarities'. They are three very different creatures and if we address only the overlap many people, albeit a small percentage of the whole, will remain ignored.
Can you have an accessible and usable website without HTML and CSS validation?
Depends on your definition of "accessible and usable".
Whose regulations? Whose requirements? Whose suggestions?
For practical purposes (as you noted) grammar validation is often one accessibility requirement. In that instance certainly and in general best practice the answer is no, you can not have an accessible and usable website without HTML and CSS validation.
However: accessible is not automatically usable, nor is usable necessarily accessible. And valid may be either, neither, or both.
However: accessible is not automatically usable, nor is usable necessarily accessible. And valid may be either, neither, or both.
lol! Give me a little time to digest the above, untwist my tongue and maybe I can come back with a reasonable response. ;) For now, I'm laying claim to your username until I figure it out. iamlost.
Is there an order to the madness?
Validation - Accessibility - Usability
What comes first? What comes last?
You won't be able to move to Priority 2 Checkpoints without validating to a DTD.
But passing the Priority 1 checkpoints still means that you can call your site accessible.
Validation - Accessibility - UsabilityWhat comes first? What comes last?
Accessibility comes first. If no one can access it, who cares if it validates or is usable. ;)