Accessibility is not only a concern for disabled people. Bots can be considered as such, like DuckDuckGo, Google or Bing. By respecting these standards, you're likely to have a better ranking. Also it helps to clean your code. Accessibility issues are often left unaddressed for budget reasons. In fact most of the cost is spent looking for errors on your website. The A11y Machine greatly help with this task, you can thus focus on fixing your code and reap the benefits. If you would like to validate your pages against the HTML5 recommendation, then you need to install Java.