Understanding SC 2.4.13: Focus Appearance (Level AAA)

Minimum area

The first part of the Success Criterion specifies a minimum area for the focus indicator:

• is at least as large as the area of a 2 CSS pixel thick perimeter of the unfocused component or sub-component

This only specifies a minimum area for the focus indicator. It does not require that the focus indicator literally be a 2 CSS pixel thick outline, only that the indicator be at least that large.

However, the simplest way to meet the size requirement is to use a focus indicator which is a solid 2 CSS pixel thick perimeter.

Using a solid outline

The easiest and most common way to meet this requirement is to use a solid outline around the component. The outline must be at least 2px thick. The following illustration shows a minimally thick focus indicator, where a 2px thick band of white pixels making up the page background around an example button have been altered to black.

For non-rectangular components, the "perimeter" definition allows authors to use either of the following types of outline:

• a line which solidly encloses a shape, or
• a line which solidly encloses the minimum bounding box of a shape

For example, a star-shaped button may use either a focus indicator that follows the shape of the star or a focus indicator that follows the bounding box of the star. In the following examples, the same three stars have already been selected, and focus is on the third star. The first example uses a focus indicator which matches the star shape of the focused star. The second uses a rectangular indicator.

Offsetting indicators slightly from the focused component, as in the examples above, is not required to meet the minimum area requirement of the success criterion, but it can help make indicators more visible. In CSS, the outline and outline-offset properties are commonly used to achieve this.

The smallest possible 2 CSS pixel thick indicator that is still a "perimeter" is a solid line that appears inside the component against the component's outer edge, for example by using a CSS border property. Indicators that are inset further within the component (not directly against the component's outer edge) need to be thicker than 2 CSS pixels to meet the minimum size requirement.

Note that different Non-text Contrast requirements may apply depending on whether the focus indicator is offset from, inset into, or against the edge of the component. See the Relationship with Non-text Contrast section below.

Other indicator shapes

This Success Criterion does not require that focus indicators be solid outlines. Other shapes may be used so long as they meet the minimum area requirement.

The minimum area of the focus indicator for a control is the area of a 2 CSS pixel thick perimeter of the control (or its minimum bounding box) in the control's unfocused state. For example, if a control is a rectangle 90px wide and 30px tall, the area of a 2 CSS pixel thick perimeter is difference between the areas of:

• A 92px by 32px rectangle (1px larger on all sides), and
• A 88px by 28px rectangle (1px smaller on all sides)

This results in a minimum area of (92px * 32px) - (88px * 28px) = 480px².

Some general formulas for 2 CSS pixel thick perimeters of common shapes are:

Rectangle with width w and height h

4h + 4w

Circle with radius r

4𝜋r

Rounded rectangle with width w, height h, and border radius r

4h + 4w - (16 - 4𝜋)r

Note

If you need to use complex mathematics to work out if a focus indicator is large enough, it is probably a sign that you should use a larger indicator instead. The bigger the visible change when an item receives focus, the easier it is for someone to see.

The following 2 examples use a 90px wide by 30px tall button, with a minimum area requirement of 480px²:

Note

Prefer using focus indicator techniques that scale with both the width and height of the focused control. Otherwise, if controls change size across different variations of a page (for example, in a responsive design), the indicator might meet the area requirement in some variations but not others. For example, in the above figure, if the width of the two highlight rectangles did not scale as the button grew wider, it would stop meeting the minimum area requirement if the button needed to grow any wider to accomodate a longer button label.

Another way of achieving the area requirement is to alter the appearance of the entire component, for instance by changing its color – provided that the new color has a contrast ratio of at least 3:1 against the original color. This can be effective in a set of closely placed buttons. The following example demonstrates this with 5 rating stars; the center star is filled in with a darker color to indicate focus. However, it is much more difficult to detect such a focus indicator when components are not near each other and so cannot be easily compared. For users using magnification, even components relatively close together may be difficult to compare, so it is not considered a best practice.

Inline links

If an inline link is broken over multiple lines, some methods of creating a focus indicator create different results by browsers. CSS outline separately surrounds each part of a link that breaks across multiple lines. It is by far the most common CSS technique for focus indication, and produces a result that satisfies the minimum bounding box definition since each part is solidly bound. CSS border will split the perimeter across the parts of the link, which results in an unenclosed border for each line of the link. The minimum bounding box definition states that link focus can be assessed as if the link was all on one line, so a 2px thick border is also considered to meet the minimum area requirement. Therefore, where the contrast requirements are met, each of these methods can produce a sufficient focus indicator.

Change of contrast

The second part of the Success Criterion's indicator requirements states that an area of the indicator:

• has a contrast ratio of at least 3:1 between the same pixels in the focused and unfocused states

This requirement measures the change of contrast between the same pixels in different states. This is different from the Text Contrast and Non-text Contrast Success Criteria, which measure the contrast between different adjacent pixels in a single state at a time.

3:1 is the minimum allowable change-of-contrast ratio, but the greater the change of contrast between states, the easier it is for users to see the focus indicator. Authors are encouraged to make the change-of-contrast ratio as great as possible.

The following illustration shows a minimally contrasting focus indicator, where some of the white pixels making up the page background have been altered to a mid-grey that has a 3:1 contrast ratio with the original white. Authors are encouraged to exceed the minimum focus appearance. For instance, the dark blue lines in figures 2 and 3 are much more visible.

When a component changes to include a focus indicator, that change can be measured as a change of color contrast. For example, if a yellow outline is added to a button on a blue background, the change of color is from blue to yellow. This change can be measured whether the focus indicator is on the background around the component, or the background within the component.

If a control receiving focus changes its background (fill color) to a color that contrasts less than 3:1 with the original background, that would not pass the change of contrast.

If the background change is sufficient, it is a method of passing the criterion.

Partially contrasting indicators

It is not necessary for the entire focus indicator to have a 3:1 change of contrast. It is sufficient for just a part of the indicator to meet the change of contrast requirement, so long as the contrasting part of the indicator meets the minimum area requirement.

When calculating whether a focus indicator meets the minimum area requirement, only the part of the indicator which meets the change-of-contrast requirement should be included in the calculation.

Gradients

If a focus indicator has a gradient, the principle is to measure the contrast of the changed area, and ignore any part of the gradient which has less than a 3:1 change-of-contrast ratio.

If you eliminate the area which has less than 3:1 change-of-contrast, you can calculate the area of the remaining parts of the indicator to determine whether the indicator meets the minimum area requirement.

Note

Some of the examples in this document are screen-captured images of elements. Due to loss of resolution in these images, the actual pixel color may not match the original. As such, they are intended to be used for illustrative purposes, and should not be inspected on a pixel-by-pixel basis for sufficient contrast.

Some designs have pages with a non-solid background image covering the whole (or part) of the page or make use of parallax scrolling effects which result in a near-infinite number of color combinations if a page is scrolled and/or changes are made to the viewport size.

If the contrast of background colors that change are close enough to need to be tested for each combination then they would likely not meet the user need of people with low vision in certain scroll combinations and would likely fail in certain combinations as well. In these cases it would be an easy solution to use a C40: Creating a two-color focus indicator to ensure sufficient contrast with all components or some other mechanism to indicate focus such as a solid box with a border to guarantee there is sufficient contrast across variations of background images or background gradients.

It is possible to use visual patterns such as strips switching places to disguise a change of focus indicator. However, this is not considered a visible indicator.

Relationship with Non-text Contrast

Focus indicators are visual information required to identify a state of a user interface component. That means that they are subject to 1.4.11 Non-text Contrast, in addition to 2.4.13 Focus Appearance.

In combination with 2.4.7 Focus Visible, 1.4.11 Non-text Contrast requires that the visual focus indicator for a component must have sufficient contrast against the adjacent colors when the component is focused, except where the appearance of the component is determined by the user agent and not modified by the author.

The difference between the contrast requirements in Focus Appearance and Non-text Contrast is:

• Focus Appearance requires that focus indicators have a change of contrast between focused and non-focused states.
• Non-text Contrast requires that focus indicators have adjacent contrast between the indicator (in the focused state) and adjacent non-indicator colors.

Additionally, Non-text Contrast does not establish any size requirement and has slightly different rules for when exceptions are allowed.

See the Relationship with Focus Visible section of Understanding 1.4.11 Non-text Contrast for more details and examples.

Component keyboard focus

The preamble to this Success Criterion is "When a user interface component has keyboard focus..." The keyboard focus is the point of interaction for someone using a keyboard. For environments with a keyboard-operable interface, the keyboard focus can be moved around the interface in order to interact with different components. Whichever component is being interacted with has focus.

WCAG defines user interface component as "a part of the content that is perceived by users as a single control for a distinct function." Because different users may perceive controls differently, there is a potential for some variation when interpreting what constitutes both a single control and a distinct function. This is particularly the case when something visually presents in a way that may differ from how it is programmatically created under the covers. Where there is not a native HTML component upon which to base designs, there can be great variations in how the components and their focus indicators are portrayed. Further, some components have sub-components that can take focus, such as the menu items on a menu.

Nonetheless, consistent results from different testers were obtained for this Success Criterion by using the focus indicator itself as the gauge of what constitutes the component being interacted with. For complex components, the three typical focus indicators are as follows:

• Focus indicator around only the whole component
• Focus indicators around both the component and subcomponent
• Focus indicator around only the subcomponent

Each of these will be discussed, using a tablist as a familiar complex component.

Focus indicator around only the whole component

When the focus indicator is shown only around the whole tablist, the user is guided to considering the tablist as a single user component. The tab items within it are visually distinguished between selected and unselected states (and visual indicators of selection state must meet the criteria given in 1.4.11 Non-text Contrast).

Having a focus indicator only around the whole is possible where there is no need to have a selected sub-component while another sub-component has focus. For a tablist which synchronizes its tab panel content with whatever tab is active, only one tab item can be selected at a time, and since whatever tab is selected is considered active, a separate focus indicator is redundant.

Result: the group focus indicator must meet the requirements of this Success Criterion.

A radio button group and a star-rating widget, which each use only a whole-component focus indicator, provide working examples of different complex components that pass the primary requirements of this Success Criterion. In the star ratings example, users can increment the rating by 1/2 stars. Not only is a focus indicator for each 1/2 star unnecessary, but it would actually be difficult to achieve without making the interaction confusing.

Focus indicators around both the component and subcomponent

For a tablist which does not keep its tab panel content synchronized with whatever tab is selected, there needs to be a focus indicator for the tab item subcomponent. This is because the tab item with focus may be different than the selected item.

The user can navigate to the tablist, which in this implementation has a focus rectangle around the whole tablist as well as one around a tab item (conventionally the item that is currently selected). The focus around the whole is helpful in cueing a keyboard user that this is a complex component that has its own interaction. The user can then move focus between the unselected and selected tab items -- each of which in turn has its own focus indicator -- before activating one, which then makes it selected as well as focused, and updates the tab panel to match.

In this scenario, either the group focus indicator or the sub-component indicator must meet the requirements of this Success Criterion. To avoid being overly prescriptive, the Success Criterion allows authors to choose which makes the most sense. Generally, if a sub-component focus is necessary, it should be assessed instead of the group indicator.

Result: the focus indicator for the tab item meets the requirements of this Success Criterion. The tablist focus indicator does not need to meet the requirements.

A slider to pick colors provides a working example of a different complex component that predominantly shows focus for the subcomponent. In this case, the thumb slider sub-component has a focus indicator of sufficient size and contrast to pass the sufficient area calculation. There is also a subtle focus around the whole slider component, but it does not need to be assessed to pass this Success Criterion.

Focus indicator around only the subcomponent

The same unsynchronized tablist can also be implemented as something which only shows focus on the tab items and not on the whole. The behaviour is the same as in the prior example, but there is never a focus indicator placed around the tablist. This interaction is acceptable, but it is not best practice since it demands more understanding from the user with less information. For example, some visual cues for the tablist and tab items (and tab panel) may not be clear. As well, keyboard users may not initially understand the expected keyboard interaction.

Result: the focus indicator for the tab item must meet the requirements of this Success Criterion, judging focus with both selected and unselected tab items.

A functional example of sub-component-only tab focus has an indicator that is large enough (at least four times the shortest side) with sufficient contrast to pass the focus area language of this Success Criterion.

Where something with focus is not a user interface component

Some pages contain very large editing regions, such as web implementations of word processors and code editors. Unlike a textarea element, which is a user interface component, these large editing regions do not typically meet the definition of user interface components; they are not "perceived by users as a single control for a distinct function." Providing focus indicators around such editing regions may still be beneficial to some; however, where the region is not perceived as a single control, it is not covered by this Success Criterion. The web page will still need to provide a insertion point (caret indicator) in such editing regions in order to meet the requirements of 2.4.7 Focus Visible.

Some non-operable elements can take focus (such as a heading element that is the target of a skip link). However, the preamble of this Success Criterion refers to user interface components; it is only when the element with focus is operable by keyboard that this Success Criterion applies.

Exceptions

There are two situations where the focus appearance does not need to be assessed:

• the focus indicator cannot be adjusted by the author
• the author has not modified the effects of the user agent default

First exception: the focus indicator cannot be adjusted by the author

The focus indicator is determined by the user agent and cannot be adjusted by the author

Some components or technologies may not allow the author to adjust the focus indicator. This is the case with HTML select elements (both single and multi-select), where the visual treatments for selection and focus cannot be adjusted by the author. In this case the Success Criterion does not apply.

Second exception: the default indicator and background are not modified

The focus indicator and the indicator's background color are not modified by the author

If the focus indicator and the background behind the focus indicator are not modified by the author, the Success Criterion does not apply.

The intent of this exception is to reduce burden on authors by allowing them to rely on the default indicators provided by user agents (browsers). If all user agents provided good focus indicators, authors would be able to concentrate efforts on other accessibility considerations. Unfortunately, browser default focus indicators vary by component, browser, and across devices and operating systems, and the default focus indicators in some browsers can be difficult to see (such as a 1px dotted outline). For this reason, most authors override browser defaults in order to overcome these deficiencies and create a more uniform user experience, regardless of browser.

Some browser makers are improving their default focus indicators to make them more visible. As more browsers adopt defaults that meet the primary bullets of this Success Criterion, authors will be able to achieve improved focus indicators without customization.

Modifying the focus indicator background

Browser default focus indicators can be made more difficult to see if the author modifies the pixels directly adjacent to the indicator (commonly referred to as its background), such as by positioning a component on top of an image or gradient background, or altering the page's default white background color, for instance using a blue background in combination with a browser's blue default indicator. For this reason, where the author alters the pixels directly adjacent to the default focus indicator, the user agent exception does not apply, and the author will need to verify they meet the size and contrast requirements of this Success Criterion.

Note

Altering the body element's background-color attribute is one way of altering the pixels directly adjacent to the indicator in most implementations. However, specifying a value of white (#FFFFFF) does not nullify this exception since, as established in the third note of the contrast ratio definition, the default ("unspecified") color is assumed to be white.

As well, if the browser provides an indicator within a component by default, then authors can potentially reduce the visibility by changing the component color (which in such a scenario is the background color for the focus indicator). For example, if the default indicator on a button uses a colored inner border, authors can negatively affect the focus appearance by making the button or its unfocused border color a similar-luminosity color. For this reason, this user agent exception can only be met if the author both does not modify the default focus indicator and does not modify its background.

Sufficient Techniques

• G195: Using an author-supplied, visible focus indicator
• C40: Creating a two-color focus indicator to ensure sufficient contrast with all components
• C41: Creating a strong focus indicator within the component

Failures

The following are common mistakes that are considered failures of this Success Criterion by the WCAG Working Group.

• F55: Failure of Success Criteria 2.1.1, 2.4.7, 2.4.13, and 3.2.1 due to using script to remove focus when focus is received
• F78: Failure of Success Criterion 1.4.11, 2.4.7 and 2.4.13 due to styling element outlines and borders in a way that removes or renders non-visible the visual focus indicator