Accessibility Conformance Testing Rules Format 1.0

1. Introduction

There are currently many test procedures and tools available which aid their users in testing web content for conformance to accessibility standards such as the Web Content Accessibility Guidelines (WCAG) [WCAG] . As the web develops in both size and complexity, these procedures and tools are essential for managing the accessibility of resources available on the web.

This format is intended to enable a consistent interpretation of how to test conformance to accessibility requirements documents and promote consistent results of in accessibility tests. It testing. The rules format is intended to be used designed to describe both manual accessibility tests as well as automated tests as performed by accessibility testing tools.

Describing Documenting how to test certain accessibility requirements will result in accessibility tests that are transparent, with test results that are reproducible. The Accessibility Conformance Testing (ACT) Rules Format defines the requirements for these test descriptions, known as Accessibility Conformance Testing Rules (ACT Rules).

2. Scope

The ACT Rules Format defined in this specification is focused on the description of designed for rules that can be used in testing content created using web technologies, such as Hypertext Markup Language [HTML] , Cascading Style Sheets [css-2018] , Accessible Rich Internet Applications [WAI-ARIA] , Scaleable Vector Graphics [SVG2] , EPUB , and more, including digital publishing. more. The ACT Rules Format is designed to be technology agnostic, meaning that it can conceivably be used to describe test rules for other technologies.

The ACT Rules Format can be used to describe ACT Rules dedicated to testing the accessibility requirements defined in Web Content Accessibility Guidelines [WCAG] , which are specifically designed for web content. Other accessibility requirements applicable to web technologies can also be testable with ACT Rules. For example, ACT Rules could be developed to test the conformance of web-based user agents to the User Agent Accessibility Guidelines [UAAG20] . The ACT Rules Format might not always be suitable to describe tests for other types of accessibility requirements.

3. ACT Rule Types

In accessibility, there are often different technical solutions to make the same type of content accessible. For example, there are multiple methods for giving an img element in HTML an accessible name. Multiple solutions could be tested in a single rule; however, such a rule tends to be quite complex, making it difficult to understand and maintain. The ACT Rules Format solves this by providing two types of rules:

• Atomic rules describe how to test a specific type of solution. It contains a precise definition of what elements, nodes or other parts "parts" of a test subject are to be tested, and when those elements are considered to fail the rule. These rules are to be kept small and atomic . Meaning that atomic rules test a single "failure condition", and do so without using the outcome findings of from other rules.

• Composite rules describe how the outcomes findings of multiple atomic rules or composite rules can be combined into a single outcome. outcome . A composite rule can have multiple "satisfying conditions", each of these provided tested in separate atomic or composite rules. The logic in the composite rule describes how any one of these satisfying conditions, or some combination of them is used to determine a single outcome.

If any one of these Not all atomic rules passes, the outcome have to be part of the a composite rule for rule. Composite rules are used when the table cell is "passed". findings of multiple rules need to be combined in order to determine (non-)conformance of a test subject to an accessibility requirement .

The separation between atomic rules and composite rules can be seen as is a division of responsibility. Atomic rules typically test if web content is correctly implemented in a particular solution. Composite rules can test if a combination of outcomes findings from other rules satisfy the accessibility requirement, in part or as a whole.

4. ACT Rule Structure

An ACT Rule MUST consist of at least the following items:

• Descriptive Title

• Rule Identifier

• Rule Description

• Rule type

• Accessibility Requirements Mapping

• Input Aspects Under Test List (for atomic rules) OR Input Rules List (for composite rules)

• Applicability

• Expectations

• Assumptions

• Accessibility Support

• Test Cases

• Change Log

• Issues List

• Acknowledgements (optional)

• Background (optional)

• ACT Rules Format outcome definition

ACT Rules MUST be written in a format that conforms to the Web Content Accessibility Guidelines [WCAG] or a comparable accessibility standard. ACT Rule test cases are allowed to contain inaccessible content. If any test case contains accessibility issues listed in WCAG 2.1 Section 5.2.5 Non-Interference , users MUST be warned of this in advance. Using an accessible format supports people with disabilities. It also makes internationalization of ACT Rules easier.

5. Rule Identifier

An ACT Rule MUST have a unique identifier that can be any unique text, such as plain text, URL or a database identifier.

6. Rule Description

An ACT Rule MUST have a description that is in plain language, and provides a brief explanation of what the rule does.

7. Accessibility Requirements Mapping

When an ACT Rule is designed to test the conformance to one or more Accessibility requirements documents , the rule MUST list all accessibility requirements from those documents that are not satisfied when the outcome of the rule is failed . For example, when designing a rule for WCAG 2.1 that tests if image buttons have an alternative text, the rule maps to success criteria 1.1.1 Non-text content, and 4.1.2 Name, Role, Value. That ACT rule will list both success criteria in the accessibility requirements mapping.

Each accessibility requirement in the mapping MUST include the following:

1. the name, title or summary of the accessibility requirement, and

2. the name of the accessibility requirements document , and

3. a link to the accessibility requirements document if one exists, and

4. the conformance level associated with the accessibility requirement, if one exists.

For each accessibility requirement in the mapping, an ACT Rule MUST indicate what the outcome of the rule means for satisfying that accessibility requirement. When the outcome is failed , the accessibility requirements are * not satisfied *. When the outcome is passed or inapplicable , the accessibility requirements could be * satisfied , or further testing could be necessary . Rules that can be used to determine if an accessibility requirement is satisfied* are called satisfying tests .

ACT Rules can be used to test accessibility requirements that are not part of a W3C accessibility standard, such as [WAI-ARIA] Hypertext Markup Language [HTML] requirements, or a testing methodology like RGAA 3 2016 . An ACT Rule MUST indictate whether or not the accessibility requirement it maps to is required for conformance in its accessibility requirements document . Examples of accessibility requirements that are not required for conformance are WCAG sufficient techniques, or a company style guide which includes both requirements and optional "best practices". That The distinction between what is required and what is optional has to be made clear.

If the failed outcome can not be mapped to not satisfied for an accessibility requirement, that requirement MUST NOT be included in the accessibility requirements mapping. The optional Background section could be used to list accessibility requirements and standards that may be thematically related, but for which the rule is not a failure test.

If the rule does not map to any accessibility requirement , the accessibility requirement mapping will only contain the explainer that it is not required for conformance to the accessibility requirements document . This is common with atomic rules used in composite rules, where accessibility requirements are only not satisfied with multiple atomic rules have the outcome failed .

8. Rule Input

The input describes what information is needed in an ACT Rule. The atomic and composite rules have different types of input.

• Atomic rules have an Input Aspects List

• Composite rules have an Input Rules List

8.1. Input Aspects Under Test List (Atomic rules only)

An aspect is a distinct part of technology used in the test subject . For example, rendering Rendering a particular piece of content to an end user commonly involves multiple different technologies, some or all of which can be of use in an [atomic rule]. Some atomic rule . For example, some rules need to operate directly on the Hypertext Transfer Protocol [http11] messages exchanged between a server and a client, while others need to operate on the Document Object Model [DOM] tree exposed by a web browser.

Atomic rules MUST list the aspects used as input for the applicability and expectations of the atomic rule. Rules can operate on several aspects simultaneously, such as both the HTTP messages and the DOM tree. Atomic rules MUST list the aspects used The method through which an input aspect is served is not relevant. For example a DOM tree can be served through HTTP as HTML, it can be bundled as several pages in the applicability EPUB , or it can be inferred from a JSX and expectations . source file. All rules that have only DOM tree as an input aspect can be applied to those technologies.

Some input aspects are already well defined in a formal specification within the context of web content, specification, such as HTTP messages, DOM tree, and CSS styling [css-2018] . These do not warrant a detailed description further than For these, a reference to the corresponding section in this specification (see Common Input Aspects under Test ). ) is sufficient as a description of the aspect. For other input aspects that are not well defined, an ACT Rule MUST include either a detailed description of the aspect in question or a reference to a well defined description.

9. 8.2. Input Rules List (Composite rules only)

A composite rule uses outcomes findings from atomic rules or other composite rules and applies a logic to them so that a single outcome can be determined for each the test target subject . The identifiers of all rules used in the expectations MUST be listed in the composite rule. The input rules list describes the input for composite rules, similar to how input aspects under test describe the input for atomic rules.

10. 9. Applicability

The applicability describes what (parts of) the test subject are tested.

10.1. 9.1. Applicability for Atomic Rules

The applicability section is a required part of an atomic rule . It MUST contain a precise description of the parts of the test subject to which the rule applies. For example, specific nodes in the DOM [DOM] tree, or tags that are incorrectly closed in an HTML [HTML] document. These are known as the test targets . The applicability MUST only use information provided through test input aspects of the same rule. No other information can be used in the applicability.

Applicability MUST be described objectively, unambiguously and in plain language.

An objective description is one that can be resolved without uncertainty, in a given technology. Examples of objective properties in HTML are element names, their computed role, the spacing between two elements, etc. Subjective properties on the other hand, are concepts like decorative, navigation mechanism and pre-recorded. Even concepts like headings and images can be misunderstood. For example, describing that the rule examines Which could refer to the tag name, the accessibility semantic role, or the element’s purpose on the web page. The latter of which is almost impossible to define objectively. When used in applicability, potentially ambiguous concepts MUST be defined objectively. This definition can be part of a larger glossary shared between rules.

10.2. 9.2. Applicability for Composite Rules

A composite rule defines how the outcomes findings from rules in its input rules list are used to determine a single outcome. outcome .

The applicability of a composite rule is defined as the union of all the applicability sections of its atomic rules as well as atomic rules that make up any composite rules in the input rules list . Rule authors MAY describe ommit the applicability for composite rules. This can be useful if it is difficult to express the combined applicability in plain language. If the composite rule includes applicability, it MUST be the union of all the applicability sections of in the atomic rules. input rules list .

Note that atomic input rules in a composite rule MAY have different applicability. Because of this, not every element applicable within the composite rule is tested by every atomic input rule.

11. 10. Expectations

An ACT Rule MUST contain one or more expectations. The expectations describe what the requirements are for the test targets derived from the applicability . 11.1. Expectations for Atomic Rules An atomic rule MUST contain one or more expectations. An expectation is an assertion about all test targets that is true about each if the test target subject (see Applicability satisfies ). the accessibility requirement . When all expectations are true for a test subject, the test subject passed the rule. If one or more expectations are false, the test subject failed the rule.

Each expectation MUST be distinct, unambiguous, and be written in plain language. Unlike in applicability, a certain level of subjectivity is allowed in expectations. Meaning that the expectation has only one possible meaning, but that meaning MAY not fully quantifiable.

When all expectations are true for a test target, Commonly, an expectation comes in the form of an "Each test target passed has ..." statement. In such an expectation, all test targets need to meet the rule. If one or more expectations are false, for the rule to pass. It is also possible to have an expectation where not all test target failed the rule. When atomic rules are used in composite rules, targets meet the outcome expectations. For example: "85% of the composite rules can be passed all test targets have an accessible name" is an expectation that is true even if the outcome of one when 15% of its constituent the test targets do not meet the expectations.

10.1. Expectations for Atomic Rules

An atomic rule is failed , depending on expectation MUST only use information available in the input aspects , from the applicability, and other expectations of the composite same rule. No other information can be used in the expectation. So for instance, an expectation could be "Expectation 1 is true and ...", but it can’t be "Rule XYZ passed and ...". This ensures that atomic rules are encapsulated.

11.2. 10.2. Expectations for Composite Rules

A When atomic rules are used in composite rules, the outcome of the composite rules can be passed even if the outcome of one of its input rules is failed , depending on the expectations of the composite rule.

All expectations of a composite rule MUST contain one or more expectations that describes describe the logic that is used to determine a single passed or failed outcome for each a test target subject , based on the outcomes of atomic rules findings or composite of rules listed in its input rules list . When all expectations are true for a test target, the test target passed the rule. If one or more expectations is false, the test target failed the rule. This works the same way for atomic rules. A composite rule expectation MUST NOT use information from test input aspects .

12. 11. Assumptions

An ACT Rule MUST list any known assumptions, limitations or any exceptions for the evaluation, the test environment, technologies being used or the subject being tested. For example, a rule that would partially test WCAG 2.0 2.1 Success Criterion 1.4.3 Contrast (Minimum) based on the inspection of CSS properties could state that it is only applicable to HTML text content stylable with CSS, and that the rule does not support images of text.

Sometimes there are multiple plausible ways that an accessibility requirement can be interpreted. For instance, it is not immediately obvious if emoji characters are "text" or "non-text content" under WCAG 2.1. Whatever the interpretation is, this MUST be documented in the rule.

While this item MUST be included in the ACT Rule, it MAY be empty when there are no known assumptions, limitations or exceptions.

13. 12. Accessibility Support

An ACT Rule MUST include known limitations on accessibility support. For example, an atomic rule that checks for a particular accessibility feature that is known not to be widely supported by assistive technologies and web browsers, or a composite rule that lists rules with known accessibility support limitations.

While this item MUST be included in the ACT Rule, it MAY be empty when there are no known accessibility support issues.

14. 13. Test Cases

Test cases are (snippets of) content that can be used to validate the implementation of ACT Rules. Each rule MUST have one or more test cases for passed , failed , and inapplicable outcome . A test case consists of two pieces of data, a snippet of each test input aspect for a rule, and the expected result from evaluating that rule. Test cases serve two functions, firstly as example scenarios for readers to understand when a rule passes, when it fails, and when it is inapplicable. It also serves developers and users of accessibility testing tools and methodologies to validate that a rule is correctly implemented.

15. 14. Change Log

It is important to keep track of changes to the ACT Rules so that users of the rules can understand if changes in test results are due to changes in the rules used when performing the tests, or from changes in the content itself. All changes to an ACT Rule that can change the outcome of a evaluation MUST be recorded in a change log. The change log can either be part of the rule document itself or be referenced from it.

Each new release of an ACT Rule MUST be identifiable with either a date or a version number. Additionally, a reference to the previous version of that rule MUST be available. For extensive changes, a new rule SHOULD be created and the old rule SHOULD be deprecated.

16. 15. Issues List (optional)

An ACT Rule MAY include a list or a reference to a list of any known issues. The issues list would be used to record cases where the outcome of an ACT Rule was failed where it ought to have been passed or inapplicable , or vice versa. There are several reasons why this might occur, including:

• Certain scenarios or the use of technologies that are very rare and were not included in the rule for that reason.

• Certain accessibility features are impossible to test within the test environment. For instance, they might only be testable by accessing the accessibility API, require screen capturing, etc.

• The scenario did not exist (due to changing technologies) or was overlooked during the initial design of the rule.

The issues list serves two purposes. For users of ACT Rules, the issues list gives insight into why an inaccurate result occurred, as well as provide confidence in the result of that rule. For the designer of the rule, the issues list is also useful to plan future updates to the rule. In a new version of the rule, resolved issues would be moved to the change log.

17. 16. Acknowledgements (optional)

An ACT Rule MAY contain acknowledgements. This can include, but is not limited to:

• List of rule authors

• List of rule reviewers/contributors

• Funding or other support

18. 17. Background (optional)

An ACT Rule MAY contain information about the background for the development of the rule, or references to relevant reading. The relationship to the relevant reading should be specified. Examples of relevant background references for a rule for a WCAG [WCAG] success criterion could be Understanding documents , WCAG Techniques , or WAI-ARIA [WAI-ARIA] , CSS [css-2018] , or HTML [HTML] specifications.

19. 18. Rule Accuracy

This section is non-normative .

While test cases can be used to determine if an ACT Rule was correctly implemented, they do not guarantee that implementations will never produce incorrect results. When writing ACT Rules, it is almost inevitable that edge cases will be overlooked. Technologies are always evolving, and content authors are constantly coming up with new and unexpected ways to use those.

There are two types of inaccuracies that can produce incorrect results. Inaccuracies in the implementation can be addressed with test cases, but inaccuracies in the ACT Rule itself can not. After all, rule inaccuracies come from the rule author being unaware of a particular edge case.

When a test result incorrectly indicates non-conformance to an accessibility requirement, this is known as a false positive. Opposite, when a rule incorrectly indicates conformance, this is a false negative. A percentage of false positives and false negatives can be calculated by comparing it to results from an accessibility audit:

• False positives : This is the percentage of test subjects , that were failed by the rule, but conform to the accessibility requirements .

• False negatives : This is the percentage of test subjects , that were passed by the rule, but were non-conformant to the accessibility requirements .

The possibility of false positives and false negatives with ACT Rules mean they will likely require ongoing maintainence. Designing a process for maintaining ACT Rules is outside the scope of the ACT Rules Format, which is limited to the rules themselves. Neverthless, it is suggested that rule authors work out a process for maintaining their rules.

20. 19. Harmonization

This section is non-normative .

While the ACT Rules Format is designed to stimulate harmonization, there are no direct requirement in the ACT Rules Format that prevent a rule author from writing rules inconsistent with already established ACT Rules. Neither are there requirements for ACT Rules to have a certain number of implementations, or to have a certain level of accuracy. This allows quality requirements to be different for different user groups, and allows them to develop over time.

Harmonization occurs when a group of rule implementors collectively accept the validity of an ACT Rule. For example, a community group of accessibility testing tool vendors could declare they’ve harmonized on a particular set of ACT Rules. Such a group can set acceptance criteria for rules, and have quality requirements that go beyond the ACT Rules Format. For example:

An example of such a process is the WCAG ACT Review Process .

21. 20. Definitions

Accessibility requirement

A requirement is a condition that has to be satisfied in order to conform to a standard, or to comply with a contract, policy or regulation. An accessibility requirement is a requirement aimed at improving access for people with disabilities to an ICT product.

A common example of accessibility requirements are the WCAG 2.1 success criteria. There are other standards, including W3C standards that include recommendations for accessibility, such as WAI-ARIA and HTML. Accessibility requirements are also often found in company policies, regional standards or in legislation.

Accessibility requirements document

A document, such as a standard, contract, policy or regulation, that includes accessibility requiremenst . For example, WCAG 2.1, WAI-ARIA 1.1, HTML 5.2, BBC HTML Accessibility Standards v2.0

Test Subject Finding

A resource or collection When evaluating a test subject using a rule, the findings of resources that can be evaluated by an ACT Rule. Example: rule are:

• An HTML page, including all embedded scripts, style and images An EPUB document A Vue component file Note : Implementers using the [EARL10-Schema] All test targets can express in the test subject with the subject property
• Which test targets met which expectations Test Target A distinct part of in the test subject . Example:
• Nodes within an HTML page A period of time within a video A range of characters within a text document Note : Implementers using the [EARL10-Schema] The outcome can express (passed, failed or inapplicble) for the test target with the pointer property subject

Outcome

One of three types of conclusions that come from evaluating an ACT Rule on a test subject . An outcome can be:

• Inapplicable : No part of the test subject matches the applicability
• Passed : The test subject meets all expectations
• Failed : The test subject does not meet all expectations

Note : While inapplicable is a valid outcome for ACT Rules, it might not be a valid result for all accessibility requirements . Notably the success criteria of WCAG 2.0 and WCAG 2.1 can only be evaluated to satisfied (passed and inapplicable) or not satisfied (failed).

Note : Implementers using the [EARL10-Schema] can express the outcome with the outcome property . In addition to passed failed and inapplicable , EARL 1.0 also defined an incomplete outcome. While this can not be the outcome of an ACT Rule when applied in its entirety, it often happens that rules are only partially evaluated. For example, when applicability was automated, but the expectations have to be evaluated manually. Such "interim" results can be expressed with the incomplete outcome.

Test Subject

A resource or collection of resources that can be evaluated by an ACT Rule.

Example:

• An HTML page, including all embedded scripts, style and images
• An EPUB document
• A Vue component file

Note : Implementers using the [EARL10-Schema] can express the test subject with the subject property

Test Target

A distinct part of the test subject .

Example:

• Nodes within an HTML page
• A period of time within a video
• A range of characters within a text document

Note : Implementers using the [EARL10-Schema] can express the test target with the pointer property

Appendix 1: Expressing ACT Rule results with JSON-LD and EARL

This section is non-normative .

Example: Output data using EARL and JSON-LD. (See Evaluation and Report Language [EARL10-Schema] and Java Script Object Notation (JSON) .)

{
  "@context": "https://raw.githubusercontent.com/w3c/wcag-act/master/earl-act.json",
  "@type": "Assertion",
  "subject": "https://example.org/",
  "test": "auto-wcag:rules/SC1-1-1-css-image.html",
  "result": {
    "outcome": "earl:failed",
    "pointer": "html > body > h1:first-child"
  }
}

Example:

{
  "@context": "https://raw.githubusercontent.com/w3c/wcag-act/master/earl-act.json",
  "@type": "Assertion",
  "subject": "https://example.org/",
  "test": "auto-wcag:SC1-1-1-css-image.html",
  "result": {
    "outcome": "earl:failed",
    "source": [{
      "test": "auto-wcag:SC1-1-1-css-image.html",
      "result": {
        "outcome": "earl:failed",
        "pointer": "html > body > h1:first-child"
      }
    }, {
      "test": "auto-wcag:SC1-1-1-css-image.html",
      "result": {
        "outcome": "earl:passed",
        "pointer": "html > body > h1:nth-child(2)"
      }
    }]
  }
}

Example: Aggregate outcomes to a WCAG success criterion

{
  "@context": "https://raw.githubusercontent.com/w3c/wcag-act/master/earl-act.json",
  "@type": "Assertion",
  "subject": "https://example.org/",
  "test": {
    "@id": "wcag20:#text-equiv-all",
    "title": "1.1.1 Non-text Content"
  },
  "result": {
    "outcome": "Failed",
    "source": [{
      "test": "auto-wcag:SC1-1-1-css-image.html",
      "result": {
        "outcome": "Failed",
        "pointer": "html > body > h1:first-child"
      }
    }, {
      "test": "auto-wcag:SC1-1-1-longdesc.html",
      "result": {
        "outcome": "Passed",
        "pointer": "html > body > img:nth-child(2)"
      }
    }]
  }
}

Example: Aggregate a list of results to a result for the website

{
  "@context": "https://raw.githubusercontent.com/w3c/wcag-act/master/earl-act.json",
  "@type": "Assertion",
  "subject": {
    "@type": ["WebSite", "TestSubject"],
    "@value": "https://example.org/"
  }
  "test": "http://www.w3.org/WAI/WCAG2A-Conformance",
  "result": {
    "outcome": "Failed",
    "source": [{
      "test": "wcag20:text-equiv-all",
      "result": {
        "outcome": "Failed",
        "source": [ … ]
      }
    }, {
      "test": "wcag20:media-equiv-av-only-alt",
      "result": {
        "outcome": "Passed",
        "source": [ … ]
      }
    }, {
      "test": "wcag20:media-equiv-captions",
      "result" : {
        "outcome": "Inapplicable",
        "source": [ … ]
      }
    }, … ]
  }
}

Appendix 2: Acknowledgments

This section is non-normative .

Participants of the AG WG active in the development of this document

Shadi Abou-Zahra, Trevor Bostic, Romain Deltour, Kathy Eng, Wilco Fiers, Alistair Garrison, Kasper Isager, Maureen Kraft, Mary Jo Mueller, Jey Nandakumar, Charu Pandhi, Stein Erik Skotkjerra, Anne Thyme Nørregaard, Kathleen Wahlbin

Enabling funders

This publication has been developed with support from the WAI-Tools Project , co-funded by the European Commission (EC) under the Horizon 2020 Program (Grant Agreement 780057). The content of this publication does not necessarily reflect the views or policies of the European Commission (EC) or any of the European Union (EU) Member States.