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The purpose of this document is to support developers of web accessibility evaluation tools by identifying typical features of those tools and how to classify them according to different combinations of those features.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

Table of contents

  1. Introduction
    1. Audience of this document
    2. Document conventions
    3. Complementary resources
  2. Typical features of an accessibility evaluation tool
    1. Types of document formats analyzed
    2. Crawling of sites
  3. Example profiles of evaluation tools
  4. References
  5. Acknowledgements
  6. Appendix A: Customising results to different audiences
  7. Appendix B: Integrating the evaluation procedure into the development testing workflows

1. Introduction

There is a wide variety of accessibility evaluation tools to be found on the web. This document intends to support the evaluation tool developers to identify their key characteristics. To do achieve that, this document:

1.1. Audience of this Document

This document is targeted mainly to development managers and developers of web accessibility evaluation tools. Under this scope, we will not distinguish between commercial and open source developers, although there are use cases that could be more relevant to one group than to the other.

A secondary audience of this document are users of accessibility evaluation tools like accessibility experts or web developers.

Examples of tools that are within the scope of the document include:

1.2. Document Conventions

The keywords must, required, recommended, should, may, and optional in this document are used in accordance with RFC 2119 [ RFC2119 ].

1.3. Complementary resources

This document must be seen in the context of several others. It is recommended that the reader reviews the following documents as well:

In the document you will find additional pointers to other resources like standards, recommendations, technical specifications, etc which are relevant to any developer interested in implementing an accessibility evaluation tool.

2. Typical features of an accessibility evaluation tool

In this section, we will describe typical features and functionalities of accessibility evaluation tools. We have tried to be as complete as possible, but it may be that some features of existing or future evaluation tools were are omitted.

It is very important that you analyse and describe for your own development process and for your customers which of those features are supported in your tool and declare any limitations of your tool.

2.1. Types of document formats analyzed

Although the vast majority of web documents are HTML documents, there are many other types of resources that need to be considered when analysing web accessibility. Of particular importance are resources like CSS stylesheets or Javascript scripts, which allow the modification of markup documents in the user agent when they are loaded or via user interaction, as many accessibility tests are the result of the interpretation of those resources.

In general, we can distinguish these types of formats:

Most of the accessibility evaluation tools concentrate on the markup validation, but the most advanced are able to process many of the types described above.

2.2. Crawling of sites

A typical difference between commercial and open source tools is the capability to crawl web resources. That means that the tool incorporates a web crawler [ WEBCRAWLER ] able to extract hyperlinks out of web resources. It must be kept in mind that, as seen in the previous section, there are many types of resources on the web that contain hyperlinks. The misconception that only HTML documents contain links may lead to wrong assumptions in the evaluation process.

A web crawler defines an starting point and a set of options. The critical features of a web crawler are related to its configuration capabilities. Among them, we can highlight:

2.3. ... Support for different accessibility compliance environments and localisation

Although there is an international effort to harmonisation of legislation in regard to web accessibility, there are still minor differences in the accessibility policy in different countries. It is important that you clearly define in your tool which of those policy environments you support. Most of the tools are focused on the implementation of their Web Content Accessibility Guidelines 2.0 [ WCAG20 ], because it is the most common reference for those policies worldwide.

Additionally it is important that you know your target market. Internationalisation and localisation are important issue to address worldwide markets. There may be cases where your customers are not able to speak English, and you need to generate information in other languages. To that end, you can start by looking into the authorised translations of the Web Content Accessibility Guidelines .

2.4. Ability to test applications, complete resources or fragments

Nowadays, it is typical that it is necessary to test fragments of HTML documents, coming for instance from a web editor in a Content Management System. For those cases, the tool must be able to generate a document fragment to be tested. Furthermore, the tool needs to filter the accessibility tests according to their relevance to the document fragment.

Within this section we include testing of web applications. For them it is typical to emulate different user actions (e.g. activating interface components or filling and sending forms) that modify the status of the current page or load new resources. The user of such an application would need to define these intermediate steps that can be later on interpreted by the tool.


3. Example profiles of evaluation tools

4. References

The following are references cited in the document.

Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. W3C Recommendation 07 June 2011. Bert Bos, Tantek Çelik, Ian Hickson, Håkon Wium Lie (editors). Available at: http://www.w3.org/TR/CSS2/
CSS Current Status is available at: http://www.w3.org/standards/techs/css#w3c_all
ECMAScript® Language Specification. Standard ECMA-262 5.1 Edition / June 2011. Available at: http://www.ecma-international.org/ecma-262/5.1/
HTML 4.01 Specification. W3C Recommendation 24 December 1999. Dave Raggett, Arnaud Le Hors, Ian Jacobs (editors). Available at: http://www.w3.org/TR/html4/
HTML5. A vocabulary and associated APIs for HTML and XHTML. W3C Candidate Recommendation 17 December 2012. Robin Berjon, Travis Leithead, Erika Doyle Navara, Edward O'Connor, Silvia Pfeiffer (editors). Available at: http://www.w3.org/TR/html5/
PDF Reference, sixth edition. Adobe® Portable Document Format, Version 1.7, November 2006. Adobe Systems Incorporated. Available at: http://www.adobe.com/devnet/pdf/pdf_reference_archive.html
Key words for use in RFC s to Indicate Requirement Levels. IETF RFC , March 1997. Available at: http://www.ietf.org/rfc/rfc2119.txt
Accessible Rich Internet Applications (WAI-ARIA) 1.0. W3C Candidate Recommendation 18 January 2011. James Craig, Michael Cooper (editors). Available at: http://www.w3.org/TR/wai-aria/
Web Content Accessibility Guidelines (WCAG) 2.0. W3C Recommendation 11 December 2008. Ben Caldwell, Michael Cooper, Loretta Guarino Reid, Gregg Vanderheiden (editors). Available at: http://www.w3.org/TR/WCAG20/
Techniques for WCAG 2.0. Techniques and Failures for Web Content Accessibility Guidelines 2.0. W3C Working Group Note 3 January 2012. Michael Cooper, Loretta Guarino Reid, Gregg Vanderheiden (editors). Available at: http://www.w3.org/TR/WCAG20-TECHS/
Wikipedia. http://en.wikipedia.org/wiki/Web_crawler


Appendix A: Customising results to different audiences

Appendix B: Integrating the evaluation procedure into the development testing workflows