Proposed Test Rule: iframe with negative tabindex has no interactive elements

Description

This rule checks that iframe elements with a negative tabindex attribute value contain no interactive elements.

Applicability

This rule applies to any iframe element that has a negative number as a tabindex attribute value.

Expectation

For each test target, the nested browsing context does not include elements that are visible and part of the sequential focus navigation. An element is “included” in a nested browsing context if its owner document is the container document of the nested browsing context.

Assumptions

This rule assumes that interactive content inside iframe elements is used to provide functionality. If the interactive content does not provide functionality, for example a button that does nothing when clicked, success criterion 2.1.1 may be satisfied, even if the rule is failed.

Accessibility Support

There are no major accessibility support issues known for this rule.

Background

By setting the tabindex attribute value of an iframe element to -1 or some other negative number, it becomes impossible to move the focus into the browsing context of the iframe element. Even though its content is still included in the sequential focus navigation, there is no way to move the focus to any of the items in the iframe using standard keyboard navigation.

Bibliography

• Understanding Success Criterion 2.1.1: Keyboard
• WCAG Technique G202: Ensuring keyboard control for all functionality

Accessibility Requirements Mapping

• 2.1.1 Keyboard (Level A)

  • Learn more about 2.1.1 Keyboard
  • Required for conformance to WCAG 2.0 and later on level A and higher.
  • Outcome mapping:
    • Any failed outcomes: success criterion is not satisfied
    • All passed outcomes: success criterion needs further testing
    • An inapplicable outcome: success criterion needs further testing
• G202: Ensuring keyboard control for all functionality

  • Learn more about technique G202
  • Not required for conformance to any W3C accessibility recommendation.
  • Outcome mapping:
    • Any failed outcomes: technique is not satisfied
    • All passed outcomes: technique needs further testing
    • An inapplicable outcome: technique needs further testing

Input Aspects

The following aspects are required in using this rule.

• DOM Tree
• CSS Styling

Test Cases

Passed

Passed Example 1

This iframe element contains no content that is part of sequential focus navigation.

<iframe tabindex="-1" srcdoc="<h1>Hello world</h1>"></iframe>

Passed Example 2

This iframe element contains a link that, because of its tabindex is not part of sequential focus navigation.

<iframe tabindex="-1" srcdoc="<a href='/' tabindex='-1'>Home</a>"></iframe>

Passed Example 3

This iframe element contains no visible content because of the small size of the iframe.

<iframe tabindex="-1" width="1" height="1" srcdoc="<a href='/'>Home</a>"></iframe>

Failed

Failed Example 1

This iframe element has a link that is part of sequential focus navigation.

<iframe tabindex="-1" srcdoc="<a href='/'>Home</a>"></iframe>

Inapplicable

Inapplicable Example 1

This iframe element does not have a tabindex attribute value that is a negative number

<iframe tabindex="0" srcdoc="<a href='/'>Home</a>"></iframe>

Glossary

Attribute value

The attribute value of a content attribute set on an HTML element is the value that the attribute gets after being parsed and computed according to specifications. It may differ from the value that is actually written in the HTML code due to trimming whitespace or non-digits characters, default values, or case-insensitivity.

Some notable case of attribute value, among others:

• For enumerated attributes, the attribute value is either the state of the attribute, or the keyword that maps to it; even for the default states. Thus <input type="image" /> has an attribute value of either Image Button (the state) or image (the keyword mapping to it), both formulations having the same meaning; similarly, “an input element with a type attribute value of Text” can be either <input type="text" />, <input /> (missing value default), or <input type="invalid" /> (invalid value default).
• For boolean attributes, the attribute value is true when the attribute is present and false otherwise. Thus <button disabled>, <button disabled="disabled"> and <button disabled=""> all have a disabled attribute value of true.
• For attributes whose value is used in a case-insensitive context, the attribute value is the lowercase version of the value written in the HTML code.
• For attributes that accept numbers, the attribute value is the result of parsing the value written in the HTML code according to the rules for parsing this kind of number.
• For attributes that accept sets of tokens, whether space separated or comma separated, the attribute value is the set of tokens obtained after parsing the set and, depending on the case, converting its items to lowercase (if the set is used in a case-insensitive context).
• For aria-* attributes, the attribute value is computed as indicated in the WAI-ARIA specification and the HTML Accessibility API Mappings.

This list is not exhaustive, and only serves as an illustration for some of the most common cases.

The attribute value of an IDL attribute is the value returned on getting it. Note that when an IDL attribute reflects a content attribute, they have the same attribute value.

Outcome

An outcome is a conclusion that comes from evaluating an ACT Rule on a test subject or one of its constituent test target. An outcome can be one of the three following types:

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

Note: A rule has one passed or failed outcome for every test target. When there are no test targets the rule has one inapplicable outcome. This means that each test subject will have one or more outcomes.

Note: Implementations 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 cannot 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.

Visible

Content perceivable through sight.

Content is considered visible if making it fully transparent would result in a difference in the pixels rendered for any part of the document that is currently within the viewport or can be brought into the viewport via scrolling.

Content is defined in WCAG.

For more details, see examples of visible.

Implementations

This section is not part of the official rule. It is populated dynamically and not accounted for in the change history or the last modified date.

Changelog

This is the first version of this ACT rule.