Iframe with interactive elements is not excluded from tab-order

Description

This rule checks that iframe elements which contain an interactive (tabbable) element are not excluded from sequential focus navigation.

Applicability

This rule applies to any iframe element that contains at least one element for which all the following are true:

the element is visible; and
the element is part of the sequential focus navigation order of the iframe’s document.

An element is contained in a nested browsing context if its owner document is the container document of the nested browsing context.

Expectation

The test target does not have a negative number as a tabindex attribute value.

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 accessibility support issues known.

Background

Setting the tabindex attribute of an iframe element to a negative value effectively excludes its content from the tab-order of the page. A button may be in the tab-order of an iframe, but if the iframe itself is taken from the tab-order, the button is effectively keyboard inaccessible.

Each document, including documents inside an iframe, has its own sequential focus navigation order. These focus orders are combined to get the page’s global tab-order (called the flattened tabindex-ordered focus navigation scope). For an iframe with a negative tabindex, its sequential focus navigation order is not included in the page’s global tab-order (as a consequence for the rules to build the tabindex-ordered focus navigation scope).

Bibliography

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.

Test Cases

Passed

Passed Example 1

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

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

Passed Example 2

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

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

Failed

Failed Example 1

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This iframe element contains a visible link that is part of its sequential focus navigation order, and has a negative tabindex.

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

Inapplicable

Inapplicable Example 1

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

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

Inapplicable Example 2

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This iframe element contains no visible content because the iframe is hidden.

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

Inapplicable Example 3

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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>

Inapplicable Example 4

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

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

Rule Versions

Latest version, 20 December 2023 (compare)
- Added inapplicable example 5 and 6
Previous version, 30 August 2023