Developers need to use a combination of techniques to perform accessibility and usability checks for their web pages. Along with code validation, accessibility checking requires human judgment. There are many tools that can help automate code validation and facilitate manual accessibility evaluation of web pages. They can check a single page or automatically spider a site or subset of a site. These tools range from code validators to browser-based tool bars and simulators.
Code validators can be configured to check against defined published standards or user defined test criteria. They come with a range of features, some only check and report errors; others report errors and suggest changes while some provide wizards to repair/retrofit the the site from within the tool.
Since validators can only check code to specified standards/criteria, they cannot make value judgments on readability and appropriateness of content. For example, while validators can check if an image includes an alt attribute, but they cannot judge if the text descriptor in the alt attribute conveys the information represented by the image.
The process for accessibility checking , therefore, cannot be totally automated and requires subjective manual verification.
Workflow to Check Web Pages for Accessibility
Validate your web pages to conform to HTML and CSS markup standards.
There are many widgets and tools that can validate the XHTML code. Tools like Tidy and W3 validators can validate HTML/XHTML code and CSS (cascading style sheets) against W3C markup standards. If a page does not meet these markup standards, they are unlikely to meet the more stringent section 508 or W3 accessibility standards.
Validate your pages to section 508 or WAI accessibility standards.
There are many tools that can validate a single page or a complete web site for accessibility against accessibility standards. At NC State, we offer Lift Machine, Lift for Desktop Solution and AccVerify that can validate web sites against user defined criteria, section 508 and/or W3C accessibility standards. These tools help identify code related issues like missing alt attributes, "skip to content" links, improper tables, forms, script errors, improper frames etc. They do not test for improper use of structural elements for presentation. Example using heading <h> element to enlarge and bold text. In addition they cannot judge the readability of content, appropriateness of text descriptors and verify captioning of audio and video content.
Verify Manually
This process is tedious and can only be done a one page at a time. However, browser accessibility features, tools bars and other widgets and tools can be used to facilitate the process. They can::
- Check read order of content by removing style sheets and tables, linearizing the page or by using a text-only browser like Lynx
- Enlarge the text and resize the window
- Check for color by looking at content in gray scale
- Check images for valid and relevant text descriptors
- Check if all activities on the page can be done from the keyboard. Example, form elements, navigation links and other interactive elements are not dependent on the mouse
- Check to see if links make sense out of context
- Check if form elements are associated with the label using <label for=> element. This can be done by clicking on the text label for the field. If it is done correctly cursor will appear in the associated field.
- Check all video and audio content for captions or text descriptors
- Use assistive technology like screen readers to check for usability of your web site
