There are several standards, and determining which ones to support depends largely on your business needs and location. The US Government for instance has Section 508 compliance while the Canadian Government has Common Look And Feel 2.0 Accessibility standards.
Generally all of these standards build upon the specifications of the W3C's Web Content Accessibility Guidelines, specifically the Priority 1 and 2 requirements.
Some examples of WCAG requirements are that all web pages must have valid HTML and CSS code, images must have alternative descriptive text, and there must be alternative methods of viewing data or accessing page functionality. Accessible browsers such as JAWS cannot interpret client scripts or view images in the way that a regular browser can, but they can still provide a spoken translation of the markup code.
What happens if you have a SharePoint site that needs to be accessible? Well, unfortunately SharePoint currently outputs a lot of non-compliant code. Luckily, there is a lot of interest in the community in finding the workarounds, and SharePoint is nothing if not flexible.
Accessibility Options Within SharePointThere seem to be a collection of elements that can go into creating a web accessible SharePoint site.
To begin with, you might wish to start with the Microsoft Minimal Master Page and a blank page layout. This will give you a fighting chance generating XHTML code, which is the first vital step. Zac Smith blogs about how to do this in detail.
Another requirement is to change the markup that the SharePoint web parts and user controls generate.
The easiest way to do this is to use a native SharePoint feature called "More Accessible Mode" that you can enable. This changes the UI rendering by applying Microsoft Active Accessibility (MSAA) standards for assistive devices. From the Microsoft Office Online site:
You turn More Accessible Mode on or off by pressing the TAB key immediately after placing focus on the page in a browser. Press the TAB key until you reach the Turn on more accessible mode or Turn off more accessible mode link. Even though the link to turn on More Accessible Mode is the first element in the tab order — which means that it is the first option that you interact with on the page — you may need to press the TAB key more than once to activate the feature.Another way to change the rendering is to rewrite the output of web and user controls.
Web Parts are generally problematic as the HTML the web parts and the web part zones render is non-compliant. User Controls however are more easily changed. You could choose to do this using delegate controls.
At run time, the delegate control on the page selects the search control that has the lowest sequence number and displays the control to the user.Another option is to use the .NET CSS Friendly Adapters that were introduced last year to help cleanup the markup the existing controls generate. John Ross (aka "Mossman") talks about this in his blog posting, "CSS Friendly Control Adapters in SharePoint 2007 (A Walk-Through)".
Client side scripts can be modified by using Regular Expressions to modify them at runtime (in the OnLoad methods of a page), but this may pose problems for future upgrades.
Third Party SolutionsHiSoftware has just announced that it will be partnering with Microsoft to create a Web Accessibility Kit for SharePoint:
The Accessibility Kit for Office SharePoint Server will include site templates, Web parts, documentation, instruction and tutorials enabling partners and customers to develop Web sites that conform to the guidelines set out in Section 508 of the U.S. Rehabilitation Act and the W3C’s Web Content Accessibility Guidelines (WCAG). The solution will also provide accessibility updates for Office SharePoint Server templates and Web parts for Web publishing, corporate intranet, team and project collaboration sites and more. This allows users to create a site and replace “out-of-the-box” MOSS components with accessibility kit templates, reusable Web content and Web parts.Telerik offers a Rich Content Editor for SharePoint that contains more accessibility options and may be worth investigating.
I've heard SiteCore recommended as a good front-end for MOSS and it could be a useful alternative to a MOSS internet portal if meeting accessibility standards is a core requirement.
Third party web part vendors may generate more compliant markup.
Finally, you can follow the Glu Mobile approach and use SharePoint as a platform to help with content management and other functionality, but build an ASP.NET application on top of it, which will give you full control over what markup is generated.