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This document lists and describes accessibility evaluation features that can be provided by web authoring, quality assurance and accessibility evaluation tools to help ensure conformance of websites to the Web Content Accessibility Guidelines (WCAG) 2.0. The main purpose of this document is to promote awareness on such accessibility evaluation features and to provide guidance for tool developers on what kind of features they could provide in future implementations of their tools. The document could also be used to help compare the features provided by different types of tools such as, for example, during the procurement of such tools.
The features in scope of this document include capabilities to help manage, carry out and report the results from accessibility evaluations. For example, some of the described features relate to crawling of websites, interacting with tool users to carry out semi-automated evaluation and providing evaluation results in machine-readable format. This document does not describe the evaluation of web content features, which is addressed by WCAG 2.0 Success Criteria.
This document encourages the incorporation of accessibility evaluation features in all web authoring and quality assurance tools, and the continued development and creation of different types of web accessibility evaluation tools. The document does not prioritize nor require any particular accessibility evaluation feature or specific type of evaluation tools.
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/.
Designing, developing, and managing a website typically involves a variety of tasks and people who use different types of tools. For example, a web developer might use an integrated development environment (IDE) to create templates for a content management system (CMS) of a website while an editor will typically use the content-editing facility provided by the CMS to create the web pages. Ideally accessibility evaluation is carried out throughout the process and by everyone involved. For example, web developers should ensure that any headings provided in templates are coded appropriately while content authors should ensure that any images added to web pages have appropriate text alternatives.
Evaluation tools can assist accessibility evaluation in many different ways. For example, tools can assist:
This document lists and describes these types of accessibility evaluation features that can be provided by evaluation tools. It does not describe the evaluation of specific web content features, which is addressed by WCAG 2.0 Success Criteria.
In the context of this document, an evaluation tool is a software application that enables its users to test web content against specific quality assurance criteria. This includes but is not limited to the following (non-mutually-exclusive) types of tools:
The accessibility evaluation features listed and described in this document can be incorporated by evaluation tools to provide support for accessibility evaluation. Section 3 provides example profiles of evaluation tools with accessibility evaluation features.
W3C Web Accessibility Initiative (WAI) provides a list of web accessibility evaluation tools that can be searched according to different criteria such as the features listed in this document.
[Review Note: Feedback on this section is particularly welcome, specifically with suggestions for accessibility evaluation features that are not listed below and with comments to refine listed accessibility evaluation features.]
The accessibility evaluation features listed and described below are not exhaustive. It may also not be possible nor desired for a single tool to implement all of the listed features. For example, tools that are specifically designed to assist designers in creating web page layouts would likely not incorporate features for evaluating the code of web applications. Developers can use this list to identify features that are relevant to their tools to plan their implementation. Also others interested in acquiring and using evaluation tools can use this list to learn about relevant features to look for.
The features of an accessibility evaluation tool are presented in the following from different perspectives: the subject to be evaluated (i.e., web content and its environment necessary to render it to the end user), the configurability of the testing functionality, the reporting customization capabilities of the tool and the integration into the development and edition workflow of the customer.
This category includes characteristics that help to render and evaluate different types of content. Due to the characteristics of the HTTP(S) protocol, the rendering of a web resource implies the manipulation of many other elements associated with it, like the request and response headers, sessions and cookies, authentication information, etc. All of them are explained in the following.
Although the vast majority of web resources are HTML documents, there are many other types of resources that need to be considered when analyzing web accessibility. For example, resources like CSS stylesheets or JavaScript scripts allow the modification of markup documents in the user agent when they are loaded or via user interaction. Many accessibility tests are the result of the interpretation of those resources and are therefore important for an accessibility evaluation.
In general, the following types of content formats can be distinguished:
The web is a multilingual and multicultural space in which information can be presented in different languages. Furthermore, this content can be transmitted using different character encodings and sets (like ISO-8859-1, UTF-8, UTF-16, ...; more information about this topic can be found in the W3C Internationalization Activity [W3Ci18n]). Accessibility evaluation tools need to process this information to be able to render these variations.
Many websites are generated dynamically by combining code templates with HTML snippets that are created by website editors. Some evaluation tools may be integrated into Content Management Systems (CMS) and Integrated Development Environments (IDE) to test these snippets as developers and/or editors create them. Usually this is done by creating DOM [DOM] document fragments from these snippets. Evaluation tools may filter as well the accessibility tests according to their relevance to the document fragment.
Web and cloud applications are becoming very frequent on the web. These applications present similar interaction patterns as those of the desktop applications and contain dynamic content and interface updates. Tools that evaluate such applications should emulate and record different user actions (e.g., activating interface components by clicking with the mouse or swiping with the fingers on a touch-screen) that modify the status of the current page or load new resources. The evaluation tool needs to define and record these intermediate steps that can be later on interpreted by the tool (see section on web testing APIs).
The identification of resources on the web by a Uniform Resource Identifier (URI) alone may not be sufficient, as other factors such as HTTP content negotiation might come into play. To support content negotiation, the testing tool customizes the HTTP headers according to different criteria to, for example, fetch particular variants of the content, such as a mobile website or a language version of a website or to control session and authentication information as presented in the following sections.
A cookie is a name-value pair that it is stored by the user-agent [HTTPCOOKIES]. Cookies contain information relevant to the website that is being rendered and often include authentication and session information, which as seen before may be relevant for content negotiation.
Websites require some times authentication (e.g., HTTP authentication, OpenID, etc.) to control access to given parts of the website or to present customized content to authenticated users.
Within HTTP, session information can be used for different purposes like, e.g., implementation of security mechanisms (login information, logout a user after a long inactivity period) or track the interaction paths of the users. Session information can be stored in the user agent local storage, in the session ID in the URL or in a cookie, for example.
There are tools that incorporate a web crawler [WEBCRAWLER] able to extract hyperlinks out of web resources. 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 most common features of a web crawler (configuration capabilities) are:
This category includes features targeted to the configuration of the tests to be performed or to the configuration of the resources to be tested.
Under this umbrella we refer to customization features that allow to configure any of the elements described in section 2.1.
Accessibility evaluation tools may offer the possibility to select a given subset of evaluation tests or even a single one. A typical example could be performing tests to the different conformance levels (A, AA or AAA) of the Web Content Accessibility Guidelines 2.0 or selecting individual tests for a single technique or common failure.
According to the Evaluation and Report Language (EARL) specification [EARL10], there are three types of modes to perform accessibility tests:
There are some evaluation tools that support accessibility experts by performing semiautomatic or manual tests. This support is normally introduced by highlighting in the source code or in the rendered document areas which could be originating accessibility problems or where human intervention is needed (for instance, to judge the adequacy of a given alternative text to an image).
Some tools do not declare that they only perform automatic testing. Since it is a known fact that automatic tests only cover a small set of accessibility issues, full accessibility conformance can only be ensured by supporting developers and accessibility experts while testing in manual and semiautomatic mode.
Developers and quality assurance engineers need sometimes to implement their own tests. For that purpose, some tools define an API so developers can create their own tests, which respond to internal demands within their organisation.
When evaluating accessibility of web sites and applications it is sometimes desirable to create scripts that emulate user interaction. With the growing complexity of web applications, there has been an effort to standardize such interfaces. One of them is, for instance, the WebDriver API [WebDriver]. With such tools, it is possible to write tests that automate the application's and users' behaviour.
This category includes features related to the ability of the tool to present, store, import, export and compare the testing results in different ways. In this section the term report must be interpreted in its widest sense. It could be a set of computer screens presenting different tables and graphics, a word processor document summarizing results, etc.
Support for standard reporting languages like EARL [EARL10] is a requirement for many customers. There are cases where tool users want to exchange results, compare evaluation results with other tools, import/export results (for instance, when tool A does not test a given problem, but tool B does it), filter results, etc.
The implementation of monitoring features requires that the tool has a persistence layer (database) where results could be stored and retrieved.
In many evaluation methodologies accessibility experts and quality assurance engineers use different tools. If the evaluation tool supports import and export of test results (for instance, in EARL format, as JSON objects, in a CSV file, etc.), it may be easily integrated in such environments.
This feature allows the customization of the resulting report according to different criteria, such as the target audience, the type of results, the part of the site being analyzed, the type of content, etc.
The presentation of evaluation results is influenced by the underlying hierarchy of the accessibility techniques with guidelines and success criteria. Aggregation is also related to the structure of the page. For instance, accessibility errors may be listed for a whole web resource or presented for concrete components like images, videos, tables, forms, etc.
Conformance statements are demanded by many customers to assess quickly the status of their website. When issuing such conformance statements it is thus necessary to tackle the different types of accessibility techniques (i.e., common failures, sufficient techniques, etc.) and aggregate results as described in the previous section.
The majority of web developers have little or no knowledge about web accessibility. Tools may provide together with their reporting capabilities additional information to support developers and accessibility experts to correct the accessibility problems detected. Such information may include examples, tutorials, screencasts, pointers to online resources, links to the W3C recommendations, etc. Automatic repair of accessibility problems is discouraged, as it may originate non-desirable side-effects.
Such support may include a guided step-by-step wizard which guides the evaluator to correct the problems found.
Accessibility evaluation tools present different interfaces, which allow their integration into the standard development workflow of the customer. The typical ones that can be highlighted are the following:
This section includes characteristics that are targeted to the customization of different aspects of the tool depending on its audience, like for instance, user interface language, user interface functionality, user interface accessibility, etc.
Localization and internationalization are important to address worldwide markets. Tool users may not be able to speak English and it is necessary to present the user interface (e.g., icons, text directionality, UI layout, units, etc.) and the reports customized to other languages and cultures. As pointed out earlier, more information about this topic can be found in the W3C Internationalization Activity [W3Ci18n] and in [I18N].
From the accessibility standpoint, it is recommended to use the authorized translations of the Web Content Accessibility Guidelines. It must be considered as well that some accessibility tests need to be customized to other languages, like for instance, those related to readability.
Typically, evaluation tools are targeted to web accessibility experts with a deep knowledge of the topic. However, there are also tools that allow the customization of the evaluation results or even the user interface functionality to other audiences like, for instance:
The availability of such characteristics must be declared explicitly and presented in an adequate way to these target user groups.
Although there is an international effort to harmonisation of legislation in regard to web accessibility, there are still minor differences in accessibility policies in different countries. The tool should specify in its documentation which policy environments are supported. Most of the tools are focused on the implementation of the Web Content Accessibility Guidelines 2.0 [WCAG20], because it is the most common reference for those policies worldwide.
Accessibility evaluation teams and web developers may include people with disabilities. To that end, it is relevant that the tool itself can be used with different assistive technologies and it is integrated with the accessibility APIs of the running operating system.
[Review Note: This section needs review once section 2 is accepted by the working group.]
As it was mentioned earlier, there is a wide landscape of accessibility evaluation tools available on the web. The following sections describe some examples of such tools. These examples do not represent any existing tool. They are provided here as illustration of how to present a profile and its features.
Tool A is a simple browser plug-in that the user can download to perform a quick automatic accessibility evaluation on a rendered HTML page. The tool tests only the Web Content Accessibility Guidelines 2.0 techniques that can be automatically analysed. Its configuration options of the tool are limited to perform one of the three conformance levels of WCAG.
After the test is run, the tool presents an alert at the side of the components where an error is found. When selecting the alert, the author is informed about the problem and hints are given on ways to solve the error. Since the tool works directly on the browser, it is not integrated in the workflow of some authors who use IDEs in their development.
Table 1 presents an overview of the matching features as described in section 2.
Tool B is a large-scale accessibility evaluation tool. It offers its users the possibility to crawl and analyze complete websites. It offers the possibility to customise which parts of the website are analysed by defining or excluding different areas of the site to be crawled. Results are persisted in a relational database and there is a dashboard to compare results at different dates.
The tool supports authentication, sessions, cookies and content negotiation by customising the HTTP headers used in the crawling process. The tool performs autonomously the WCAG automatic tests.
The tool offers a customized view, where experts can select a subset of the crawled pages and complete the automatic and semiautomatic tests by inspecting the selected pages and store the results in the database.
The reports of the tool can be exported as a EARL report (serialized as RDF/XML), in a spreadsheet and as a PDF document.
The tool incorporates the corresponding interfaces to the accessibility APIs of its operating system.
Table 1 presents an overview of the matching features as described in section 2.
Tool C is an accessibility evaluation tool for web-based mobile applications. The tool does not support native applications, but it provides a simulation environment that gives access to the application to the Device API.
The tool can emulate different user agents running on different mobile operating systems. It also shows typical display sizes corresponding to mainstream smartphones and tablets. It supports HTML, CSS and JavaScript, providing to the testers and implementation of the Web Driver API, supporting automatic and manual evaluation.
This section presents a tabular overview of the characteristics of the tools described previously.
Category | Feature | Tool A | Tool B | Tool C |
---|---|---|---|---|
Test subjects and their environment | Content-types | HTML (CSS and JavaScript interpretation is provided because the plug-in has access to the rendered DOM within the browser) | HTML and CSS only | HTML, CSS and JavaScript |
Content encoding and language | yes | yes | yes | |
Document fragments | no | no | no | |
Dynamic content | yes | no | yes | |
Cookies | yes | yes | yes | |
Authentication | yes | yes | yes | |
Session tracking | no | yes | yes | |
Content negotiation | no | yes | yes | |
Crawling | no | yes | no | |
Test customization | Customization of the performed tests | no | yes | nno |
Semiautomatic and manual testing | no | yes | yes | |
Development of own tests and test extensions | no | no | no | |
Web testing APIs | no | no | yes | |
Reporting | Standard reporting languages | no | yes | no |
Report customization and filtering according to different criteria | yes | yes | no | |
Conformance and results aggregation | no | yes | yes | |
Tool audience | Localization and internationalization | no | no | yes |
Functionality customization to different audiences | no | yes | no | |
Policy environments | no | no | no | |
Tool accessibility | no | yes | no | |
Monitoring and workflow integration | Error repair | yes | no | yes |
Integration in the web development workflow | no | yes | no | |
Persistence of results and monitoring over time | no | yes | yes |
The following are references cited in the document.
The editors would like to thank the contributions from the Evaluation and Repair Tools Working Group (ERT WG), and especially from Yod Samuel Martín, Christophe Strobbe, Emmanuelle Gutiérrez y Restrepo and Konstantinos Votis.