Evaluating Web accessibility at different processing phases

Abstract

Modern Web sites use several techniques (e.g. DOM manipulation) that allow for the injection of new content into their Web pages (e.g. AJAX), as well as manipulation of the HTML DOM tree. This has the consequence that the Web pages that are presented to users (i.e. after browser processing) are different from the original structure and content that is transmitted through HTTP communication (i.e. after browser processing). This poses a series of challenges for Web accessibility evaluation, especially on automated evaluation software. This article details an experimental study designed to understand the differences posed by accessibility evaluation after Web browser processing. We implemented a Javascript-based evaluator, QualWeb, that can perform WCAG 2.0 based accessibility evaluations in the two phases of browser processing. Our study shows that, in fact, there are considerable differences between the HTML DOM trees in both phases, which have the consequence of having distinct evaluation results. We discuss the impact of these results in the light of the potential problems that these differences can pose to designers and developers that use accessibility evaluators that function before browser processing.

Keywords:

• Web science
• Web accessibility
• Web browser processing
• Automated evaluation

Notes

1. Node.js: http://nodejs.org.

2. V8 Javascript engine: http://code.google.com/p/v8/.

3. GitHub modules: https://github.com/ry/node/wiki/modules.

4. CURL: http://curl.haxx.se/.

5. http://www.phantomjs.org/.

6. Alexa Top 500: http://www.alexa.com/topsites [24 September 2011].