With all the various issues that need to be considered when ensuring accessible web design some of the more basic measures that help the accessibility and useability of a site can be overlooked. One of the most useful measures in terms of providing a user friendly experience for visitors who are having problems browsing your site is the use of custom error pages.
Error pages are a response code provided by HTTP to inform users of the site that there is a problem. Probably the most common of these is the HTTP 404 error code or “page not found” which occurs when a web page being browsed to is unavailable. Other common error message codes are 403 (used when someone tries to access a forbidden or unavailable section of a website) and 500 (when there is a web server issue). These messages can be confusing or intimidating to internet novices. And even for users who have seen them many times before, the default error messages provide little information or accessibility and useability of the rest of the site.
If on this site you tried to direct to a page such as abcdef.aspx you would receive this site’s custom 404 error message. This is integrated into the overall look and feel of the site, offers a plain English explanation of the problem and direct links to the main home page and the site search. In this way, even if someone browses to an unavailable page they are not excluded from the rest of the site, and can continue to browse. It also acts to demonstrate to some browsing directly to a page on Fog of Eternity (perhaps from an outdated link on a search engine or similar) that while the specific page they are looking for is not there, the site is still up and running.
Configuration of custom error pages is largely dependent on the way that a site is put together. Many web hosts provide the ability for users to define web addresses for custom error pages, while the likes of ASP.NET uses Page_Error, Application_Error or the web.config file. I use the web.config file currently to define a custom 404 error page (the most likely page to be called into regular use), while I define a wider and more comprehensive error handling system for the site overall.
But the point really is the importance of something as simple as custom error pages. They can add greatly to the accessibility and general user-friendliness of a site, are usually easy to define and set up, and shouldn’t be overlooked.