On Web Accessibility Environments

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1. On Web AccessibilityEvaluation Environments W4A 2011 Nádia Fernandes, Rui Lopes, Luís Carriço {nadia.fernandes,rlopes,lmc}@di.fc.ul.pt 2. Introductionã Web…
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  • 1. On Web AccessibilityEvaluation Environments W4A 2011 Nádia Fernandes, Rui Lopes, Luís Carriço {nadia.fernandes,rlopes,lmc}@di.fc.ul.pt
  • 2. Introduction• Web Accessibility is tripartite: Page semantics, Assistive Technologies, Browser capabilities• Modern Web development transcends static HTML• Evaluation tools (typically) stay outside the browser• Goal: to study the impact of evaluating accessibility in the browser
  • 3. Web Browsing• Web page, first HTTP response• Resources, ancillary transformations (CSS, Javascript)• AJAX, browsing-time transformations
  • 4. Hypothesis Evaluating Web content in the browser provides moreaccurate and more in-depth analysis of its accessibility. • Need for understanding the differences and limitations of evaluation environments • Evaluation process (i.e., its implementation) must be the same in both environments, for comparison purposes
  • 5. WebAccessibilityEvaluationEnvironments
  • 6. Implementation• Javascript, same techniques (18) in both environments• Results transformed into EARL & CSV• Execution in each environment at respective timings: Command line, Browser, after HTTP GET bookmarklet
  • 7. Testability & Validation• Testbed with 102 HTML documents• Implementation returns the same results in both environments, for the same HTML document
  • 8. Experimental Study• Analysis of evaluation results in both environments• 82 homepages from Alexa Top 100 Web sites
  • 9. Data Acquisition and Processing • Time between HTTP GETs, 89.72s (σ ≈ 70s) • Document size average: • Command line, 70KB (σ ≈ 95KB) • Browser, 81KB (σ ≈ 127KB) • Document HTML element count average: • Command line, 915 elements (σ ≈ 95KB) • Browser, 1154 elements (σ ≈ 95KB)
  • 10. The differences of an HTMLdocument in both environments was observed, and is significative.
  • 11. Results: Average Outcomes Successes • Command line, 9.67 elements (σ ≈ 19.12) • Browser, 272.78 elements (σ ≈ 297.10) Failures • Command line, 47.44 elements (σ ≈ 70.82) • Browser, 90.10 elements (σ ≈ 125.93) Warnings • Command line, 425.02 elements (σ ≈ 682.53) • Browser, 685.21 elements (σ ≈ 1078.10)
  • 12. Results: Incorrect Outcomes• False positives and false negatives were found in Command line evaluation• 67% of the criteria yielded false negatives
  • 13. Results: Criterion 1.1.1• Availability of alternative text content• We detected a high increase of scripted image injection
  • 14. Results: Other CriteriaCriterion 1.2.3 (Media alternatives)Almost all occurrences in the browserCriterion 2.4.4 (Link purpose)One case of false positives detectionCriterion 3.2.2 (On submit buttons)Some cases where buttons were injected
  • 15. Conclusions• Accessibility evaluation study of 82 homepages from Alexa Top 100 Web sites• Compare evaluation environments• Scripts alter Web pages in a significant way• Accessibility evaluation is affected, both on incorrect and incomplete results in Command line environment
  • 16. Limitations• Possibility of artifacts introduced between requests for same Web page• Analysis of HTML DOM tree• Impossibility to check if a given individual result occurs in both environments• Automated evaluation yields limited results
  • 17. Ongoing Work• Implementation of post-cascading and post- content flow CSS-aware techniques• Continuous monitoring of DOM manipulation (to, e.g., detect live regions)• Detection of differences between DOM trees, to pinpoint results
  • 18. Thank yourlopes@di.fc.ul.pt
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