The last few exciting chapters in our dynamic WCAG adventure have concerned the various guidelines of Principle 3, which stresses the importance of making information and the operation of user interface understandable. Now, we will move onto Principle 4, in which we'll go over how to ensure that the content of your site is robust enough to work reliably in a number of browsers and user agents, including assistive technologies. Guideline 4.1 outlines ways to maximize your site's compatibility with any current or future user agents and assistive technologies.
It's essential that user agents be able to properly interpret and parse content on your site. Content implemented using a markup language should be created according to the rules of that language's formal grammar. Specifically, this means:
In all cases, if you can determine that specifications allow any of these features, then the rule can be disregarded.
The best way to ensure that the content on your site is set according to the formal grammar of the markup language you're using is to utilize an online or offline validator. The resources tab on the WCAG site linked here lists a number of validating options for HTML and XML.