CSS Spatial Navigation Level 1

This specification is rather long. To make it easier to read and focus on a particular area, a few checkboxes are provided below. Checking them hides part of the specification. This is only meant as a reading aid, the specification remains the full document.

1. Introduction

This section is not normative.

Historically, most browsers have not offered features to let the user move the focus directionally. Some, such as TV browsers, have enabled the user to move the focus using the arrow keys out of necessity, since no other input mechanism is available on a typical TV remote control.

Others have enabled different key combinations to control spatial navigation, such as pressing the Shift key together with arrow keys.

This ability to move around the page directionally is called spatial navigation.

Spatial navigation can be useful for a web page built using a grid-like layout, or other predominantly non linear layouts. The figure below represents a photo gallery arranged in a grid layout. If the user presses the Tab key to move focus around the images, they need to press the key many times to reach the desired image element.

Also, spatial navigation moves the focus to the predictable element for users because it moves the focus among focusable elements depending on their position. Sometimes elements on the page aren’t arranged independently of their source order. Therefore unlike spatial navigation, sequential navigation using the Tab key makes focus navigation unpredictable.

While arrow keys are naturally suited to control spatial navigation, no previous specification describes how that should work, or how it may be controlled. This specification introduces a processing model for spatial navigation, as well as APIs enabling the author to control and override how spatial navigation works.

Note: Some aspects of this specification, such as the JavaScript Events and APIs could also be extended to sequential navigation, in order to make sure that keyboard navigation has a consistent and well defined model in general.

Note: As a general principle, keyboard navigation, and spatial navigation in particular, should be possible to use and control without JavaScript, and declarative solutions are therefore preferred. Since spatial navigation depends on layout, that means CSS is typically the right mechanism to define spatial navigation related controls. However, in the spirit of the Extensible Web Manifesto [EXTENSIBLE], we feel it is important to provide the right JavaScript primitives to let the author experiment and explore the problem space. More declarative features may be added later, based on feedback and experience acquired through such JavaScript usage.

Note: A few features are marked at-risk. The editors of this specification believe they represent an important part of the user or author experience of the features defined in the specification. At the same time, the core functionality of this specification can be implemented without implementing these so it seems possible that implementers may choose to down-prioritize them to reduce the scope of the first implementation. While it is hoped that these features will be implemented as well, they are marked at-risk in recognition that they might not be at first.

2. Module interaction

This document depends on the Infra Standard [infra].

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119. [RFC2119]

3. Overview

This section is not normative.

Using a UA-defined mechanism (typically arrow keys, possibly in combination with modifier keys like Shift or Control), the user may ask the user agent to navigate in a particular direction. This will either move the focus from its current location to a new focusable item in the direction requested, or scroll if there is no appropriate item.

More specifically, the user agent will first search for visible and focusable items in the direction indicated within the current spatial navigation container (by default, the root element, scrollable elements, and iframes, but other elements can be made into spatial navigation containers using the spatial-navigation-contain property).

If it finds any, it will pick the best one for that direction, and move the focus there.

If it does not, it will scroll the spatial navigation container in the requested direction instead of moving focus. Doing so may uncover focusable elements which would then be eligible targets to move the focus to next time spatial navigation in the same direction is requested.

If the spatial navigation container cannot be scrolled, either because it is not a scrollable element or because it is already scrolled to the maximum in that direction, the user agent will select the next spatial navigation container up the ancestry chain, and recursively repeat the above process until it finds some element to focus or scroll, or reaches the root element.

Note: As a consequence of this processing model, the elements that are reachable by sequential navigation and by spatial navigation are almost the same. Elements that are currently outside of the viewport of a scrollable element can only be reached by spatial navigation once they have been scrolled into view. Therefore, elements that cannot be scrolled into view by default.

At key points during this search for the appropriate response to the spatial navigation request, the user agent will fire events. These enable the author to prevent the upcoming action (by calling preventDefault()), and if desired to provide an alternate action, such as using the focus() method on a different element of the author’s choosing.

To help the author write such alternate actions, and as part of exposing underlying platform primitives as per the Extensible Web principles, this specification also defines JavaScript APIs that expose key constructs of the underlying model.

See § 5 JavaScript API for details about the JavaScript API, § 6.2 Navigation Event Types for details about the various events, and § 9 Controlling spatial navigation through declarative means for details about the CSS properties.

This example shows how a series of focusable elements arranged in a scrollable element would be navigated when using spatial navigation. For the sake of keeping the description simple, this example assumes a user agent where spatial navigation is triggered using arrow keys.

On the left of figure 2, "Box 2" is focused. Pressing the ArrowDown key moves the focus to "Box 3" without scrolling because "Box 3" is visible in the scrollport of the spatial navigation container.

On the first of figure 3, under "Box 3", there isn’t any visible element in the scrollport. Therefore, the effect of pressing the ArrowDown is to scroll down, as shown in the second. The next press of the ArrowDown key makes "Box 4" come into the scrollport, and the focus will move to it when there is additional pressing the ArrowDown, as the fourth.

This example uses the markup as follows:

#scroller {
    width: 700px;
    height: 700px;
    overflow-x: hidden;
    overflow-y: auto;
}

.box {
    width: 150px;
    height: 110px;
    background-color: blue;
}

.box:focus {
    background-color: red;
}

<div id="scroller">
    <div class="box" tabindex="0">Box 1</div>
    <div class="box" tabindex="0">Box 2</div>
    <div class="box" tabindex="0">Box 3</div>
    <div class="box" tabindex="0">Box 4</div>
</div>

4. Triggering Spatial Navigation

When the user triggers spatial navigation in a given direction, the user agent must run the spatial navigation steps in that direction.

This specification does not define what UI mechanism user agents should offer to users to trigger spatial navigation. This intentionally left for user agents to decide.

Although user agents can implement the processing model and APIs defined by the specification, this specification recommends that user agents should offer a means for users to trigger spatial navigation directly, without having to use the APIs.

Note: Conversely, the author should assume that spatial navigation may be triggered by the user agent in response to user actions even if the author has not invoked any of the APIs.

Regardless of the actual mechanism chosen to trigger spatial navigation, the following requirements apply:

• If the mechanism the user must use to trigger spatial navigation would normally fire a UIEvent, the event must be fired prior to running the spatial navigation steps and these steps must not be run if that event’s canceled flag gets set.

  Gaming devices may trigger spatial navigation based on pressing the D-pad. This would result in firing a keydown event with the key set to one of ArrowDown, ArrowLeft, ArrowRight, or ArrowUp, followed if not canceled by running the spatial navigation steps, including firing the relevant NavigationEvents.

  A user agent on a desktop computer that triggers spatial navigation using the arrow keys of the keyboard would follow the same sequence.

• If the mechanism the user must use to trigger spatial navigation would also perform other actions in some contexts, the user agents should in these contexts give priority to these other actions and execute them instead of spatial navigation. It must not trigger both.

  In a user agent that triggers spatial navigation using the arrow keys without modifier keys, and uses these same arrow keys to move the text insertion caret when an editable element is focused, the arrow keys should by default to moving the caret. Spatial navigation would only be triggered by the arrow keys when the focused element is not editable or when it is editable, but the caret cannot move any further in the requested direction.

  An exception is made for scrolling: since spatial navigation itself handles scrolling (in addition to moving the focus) user agents should not offer the same mechanism to trigger both spatial navigation and the scrolling behavior separate from spatial navigation. However, user agents may offer a way for the user to switch between different modes, or offer both based on different UI mechanisms.

  A user agent may have a setting to let the user choose between using the arrow keys without modifier keys for spatial navigation or for scrolling. Another one may offer scrolling on arrow keys without modifiers, and spatial navigation on arrow keys when pressed together with the Shift key, or on the W A S D keys. Offering only spatial navigation or only scrolling as responses to pressing arrow keys would also be possibilities.

5. JavaScript API

5.1. Triggering Navigation Programmatically

The navigate() method enables the author to trigger spatial navigation programmatically, as if the user had done so manually (for instance, by pressing the arrow keys in a browser where that is the way to trigger spatial navigation).

Note: As this triggers the same processing model as manual navigation, all the same results should be expected: the same chain of events will be fired and the same element will be scrolled or focused.

Note: The author can use this to trigger spatial navigation based on a different UI mechanism than the one assigned by the user agent, such as mapping to different keys, or triggering spatial navigation from a clickable on-screen directional pad, or in reaction to other events than UI ones. It could also be used when an author wants to interrupt navigation to do some asynchronous operation (e.g. load more content in an infinite scroller) then resume the navigation where they canceled.

Note: This API is also useful for testing purposes, as there it is difficult to trigger spatial navigation that does not depend on vendor specific UI conventions.

enum SpatialNavigationDirection {
    "up",
    "down",
    "left",
    "right",
};

partial interface Window {
    undefined navigate(SpatialNavigationDirection dir);
};

When the navigate(dir) method is called, the user agent must run the following step:

• If direction dir is "up", "down", "left", or "right", run the spatial navigation steps in dir.

The name of this API is under discussion [Issue #3387]

5.2. Low level APIs

These APIs are designed to be low level constructs following the processing model closely. As such, they should be easy to use by the author who wants to extend or override the way spatial navigation works.

enum FocusableAreaSearchMode {
    "visible",
    "all"
};

dictionary FocusableAreasOption {
    FocusableAreaSearchMode mode;
};

dictionary SpatialNavigationSearchOptions {
    sequence<Node>? candidates;
    Node? container;
};

partial interface Element {
    Node getSpatialNavigationContainer();
    sequence<Node> focusableAreas(optional FocusableAreasOption option = {});
    Node? spatialNavigationSearch(SpatialNavigationDirection dir, optional SpatialNavigationSearchOptions options = {});
};

Note: The way the direction is expressed allows us to expand to more than 4-way navigation later if this is found necessary. More directional keywords or a numerical angle could be added.

Note: the focusableAreas() and getSpatialNavigationContainer() methods are at-risk.

When these methods are called, the user agent must run the steps described below:

getSpatialNavigationContainer()

1. Return the nearest ancestor of the element that is a spatial navigation container, or the document if the nearest spatial navigation container is the viewport.

Note: If the element is a spatial navigation container, getSpatialNavigationContainer() also returns the nearest spatial navigation container, not the element itself.

focusableAreas(option)

1. Let visibleOnly be false if option is present and its value is equal to all, or true otherwise.

2. Let areas be the result of finding focusable areas within the element with visibleOnly as argument.

3. Return areas

The following code shows how to get all the visible focusable elements in the current page using focusableAreas(). If the method finds a spatial navigation container, it recursively finds focusable areas inside it. Because the value of the mode attribute in this method is visible, the focusable elements which aren’t inside the scrollport are excluded from the result.

<body>
    <button></button>
    <div style="width:300px; height:200px; overflow-x: scroll;">
        <button style="left:25px;"></button>
        <button style="left:150px;"></button>
        <button style="left:350px;"></button>
    </div>
</body>

const focusableAreas = document.body.focusableAreas({mode: 'visible'});
focusableAreas && focusableAreas.forEach(focusable => {
  focusable.style.outline = '5px solid red';
});

The figure below is the result of this code.

spatialNavigationSearch(dir, options)

1. Let direction be the value of dir.

2. Let container be

   • if the value of container attribute of options is not null,

     • itself, if it is spatial navigation container.

     • its nearest spatial navigation container ancestor, otherwise.

   • else the element’s nearest spatial navigation container ancestor.

3. Let areas be

   • the value of candidates attribute of options if it is not null,

   • result of finding focusable areas within container otherwise.

4. Return the result of selecting the best candidate among areas within container in direction from the element.

Note: When neither a container nor a list of candidates is provided, this only searches through the visible focusable areas of the nearest spatial navigation container ancestor. If there isn’t any, this does not climb further up the ancestry chain, and the result will be null.

6. Navigation Events

6.1. Interface NavigationEvent

The NavigationEvent interface provides specific contextual information associated with spatial navigation.

To create an instance of the NavigationEvent interface, use the NavigationEvent constructor, passing an optional NavigationEventInit dictionary.

[Exposed=Window]
interface NavigationEvent : UIEvent {
    constructor(DOMString type,
                optional NavigationEventInit eventInitDict = {});
    readonly attribute SpatialNavigationDirection dir;
    readonly attribute EventTarget? relatedTarget;
};

dictionary NavigationEventInit : UIEventInit {
    SpatialNavigationDirection dir;
    EventTarget? relatedTarget = null;
};

6.2. Navigation Event Types

This section and its subsections are not normative.

The Navigation event types are summarized below. For full normative details, see § 8 Processing Model.

6.2.1. navbeforefocus

This event occurs when there is a valid result of selecting the best candidate.

Type	navbeforefocus
Interface	NavigationEvent
Bubbles	Yes
Cancelable	Yes
Attributes of the event	Event.target The focused element or if no element focused, then the body element if available, otherwise the root element NavigationEvent.relatedTarget The DOM anchor of the focusable area that will be focused NavigationEvent.dir The direction of the navigation as requested by the user

The user agent dispatches navbeforefocus event before spatial navigation moves the focus. The event target is the element which has focus and the relatedTarget is the element which is about to receive focus.

If navigation-override is disabled in the node document of eventTarget for the origin of the active document of the top-level browsing context, this event won’t be dispatched.

This example shows the event order when pressing the ArrowRight key. For the sake of keeping the description simple, this example assumes a user agent where spatial navigation is triggered using arrow keys.

	Event type	KeyboardEvent.key	Notes
1	keydown	ArrowRight	MUST be a key which can activate spatial navigation, such as the arrow keys, or spatial navigation is not activated.
2	navbeforefocus		Sent if the candidates for spatial navigation is not null, or this is not generated.
3	focusin		Sent before the target element receives focus.
4	focus		Sent after the target element receives focus.

The following code changes the behavior of spatial navigation so that when a scroll container would get focused, if it has at least one visible focusable descendant, the focus is automatically transferred to it, recursively.

document.addEventListener('navbeforefocus', e => {
    e.preventDefault();

    let nextTarget = e.relatedTarget;
    if (isSpatialNavigationContainer(nextTarget)) {
        const areas = nextTarget.focusableAreas();

        if (areas.length > 0) {
            nextTarget = nextTarget.spatialNavigationSearch(e.dir, { candidates: areas });
        }
    }
    nextTarget.focus();
});

function isSpatialNavigationContainer(element) {
    return (!element.parentElement) ||
        (element.nodeName === 'IFRAME') ||
        (isScrollContainer(element)) ||
        (isCSSSpatNavContain(element));
}

6.2.2. navnotarget

This event occurs before going up the tree to search candidates in the nearest ancestor spatial navigation container when spatial navigation has failed to find any candidate within the current spatial navigation container, and in cases where the spatial navigation container is scrollable, when it cannot be scrolled further.

Type	navnotarget
Interface	NavigationEvent
Bubbles	Yes
Cancelable	Yes
Attributes of the event	Event.target The focused element or if no element focused, then the body element if available, otherwise the root element NavigationEvent.relatedTarget The spatial navigation container that was searched in. NavigationEvent.dir The direction of the navigation as requested by the user

The user agent dispatches navnotarget event with initializing the event target as the element which has focus and the relatedTarget as spatial navigation container of the event target.

If navigation-override is disabled in the node document of eventTarget for the origin of the active document of the top-level browsing context, this event won’t be dispatched.

This example shows the event order when pressing the ArrowDown key in the situation like the following figure. For the sake of keeping the description simple, this example assumes a user agent where spatial navigation is triggered using arrow keys.

	Event type	Event target	relatedTarget	Notes
1	keydown	#box2	N/A	MUST be a key which can activate spatial navigation, such as the arrow keys, otherwise spatial navigation is not triggered.
2	navnotarget	#box2	#scrollContainer	Sent if #scrollContainer doesn’t contain any candidate and cannot be scrolled, otherwise this would not be generated.
3	navbeforefocus	#box2	#box3	Sent if the candidates in #container is not null, otherwise this would not be fired.
4	focusin	#box3	#box2	Sent before the target element receives focus.
5	focus	#box3	#box2	Sent after the target element receives focus.

The result of this example is the figure as follows:

This example uses the markup as follows:

#container {
    width: 900px;
    height: 1400px;
}

#scrollContainer {
    width: 700px;
    height: 700px;
    overflow-x: hidden;
    overflow-y: auto;
}

.item {
    width: 150px;
    height: 110px;
    background-color: blue;
}

.item:focus {
    background-color: red;
}

<div id="container">
    <div id="scrollContainer">
        <div id="box1" class="item" tabindex="0">Box 1</div>
        <div id="box2" class="item" tabindex="0">Box 2</div>
    </div>
    <div id="box3" class="item" tabindex="0">Box 3</div>
</div>

The following code changes the behavior of spatial navigation to trap the focus within a spatial navigation container which is vertically scrollable. When no further focusable elements can be found in the requested direction and the spatial navigation container cannot be scrolled any further, the focus loops back to the other side instead of moving outside of it.

However, the focus can still be moved outside by sequential navigation, mouse interaction, or programmatic calls to focus().

scrollContainer.addEventListener('navnotarget', e => {
    let nextTarget = null;
    const verticalDir = ['up', 'down'];
    const candidates = e.relatedTarget.focusableAreas({'mode': 'all'});

    // Prevent default only when navigation direction is on y-axis
    if (verticalDir.includes(e.dir) && (candidates.length > 0)) {
        e.preventDefault();

        if (e.dir === 'down') {
            nextTarget = candidates[0];
        } else if (e.dir === 'up') {
            nextTarget = candidates[candidates.length-1];
        }
        nextTarget.focus();
    }
});

7. The navigation-override policy-controlled feature

The navigation-override policy-controlled feature controls the availability of mechanisms that enables the page author to take control over the behavior of spatial navigation, or to cancel it outright.

• The feature name is "navigation-override"

• The default allowlist for navigation-override is "self"

As defined in further details in § 8.3 Navigation, if navigation-override is disabled in a document, the navigation events (see § 6 Navigation Events) will not be fired.

Note: This is to prevent a hostile iframe from using these events in order to hijack the focus. We recognize that there exist other mechanisms predating spatial navigation that malicious the author could use to interfere with the user’s ability to control where the focus goes. Despite that, it seems worthwhile to attempt not to increase this attack surface, although it is possible that such attacks are already sufficiently easy to perform that this is a lost cause. Further feedback on this topic, based on experience with implementation or with mitigating such attacks, is very welcome.

8. Processing Model

8.1. Glossary

The following term definitions have been specified to explain the processing model for spatial navigation. See the links within the definitions for more information.

The boundary box of an object is defined as follows:

• if the object is a point, the boundary box is that point

• if the object is a box or box fragment, the boundary box is the border box of that box or fragment

• if the object is a focusable area which is not an element, the boundary box is the axis-aligned the bounding box of that focusable area

The inside area of an object is defined as follows:

• if the object is a scroll container, its optimal viewing region

• if the object is a document, the viewport of its browsing context

• if the object is a box or box fragment, its boundary box

• otherwise, the optimal viewing region of its nearest ancestor scroll container

NOTE: If an object is offscreen, the inside area should be the nearest visible ancestor container.

CSS should have a term for “border box taking into account corner shaping properties like border-radius”. [Issue #w3c/csswg-drafts#2324]

The search origin is the origin for searching next target.

The spatial navigation starting point is the origin for searching next target which is set by the user agent. It is initially unset and it can be element or point.

Note: For example, the user agent could set it to the position of the user’s click if the user clicks on the document contents, and unset when the focus is moved (by spatial navigation or any other means).

If the user agent sets both a spatial navigation starting point and a sequential focus navigation starting point, they must not be set differently.

8.2. Groupings of elements

While the processing model for spatial navigation is to work from the layout of the document and the relative position of focusable elements, the user agent is required to prioritize finding elements from a local logical grouping, only looking for focusable elements outside of the grouping if a suitable one cannot be found inside it (see § 8.3 Navigation for details).

Such groupings are called spatial navigation containers.

By default, spatial navigation containers are established by:

• The viewport of a browsing context (not limited to the top-level browsing context)

• scroll containers

8.3. Navigation

The processing model for spatial navigation describes how spatial navigation works in general.

8.4. Focus Navigation Heuristics

Note: The following algorithms are inspired from Chrome’s implementation as well as from the old WICD Spec. Implementors who find better approaches or refinements to these approaches are strongly encouraged to provide feedback and help improve this specification in order to maximize interoperability. In particular, divergences in how user agents find focusable areas may cause some elements to be focusable in some user agents but not in others, which would be bad for users.

All geometrical operations in this section are defined to work on the result of CSS layout, including all graphical transformations, such as relative positioning or [CSS-TRANSFORMS-1].

distance = euclidean + displacement - alignment - sqrt(Overlap)

<div>
    <button>Previous Week</button>
    <table>
        <tr><td><th>M<th>T<th>W<th>T<th>F<th>S<th>S
        <tr><td>0-6<td><td><td><td><td><td><td><a href="#">Foo</a>
        <tr><td>6-9<td><a href="#">Bar</a><td><td><td><td><td><td>
        <tr><td>9-12<td><td><a href="#">Bat</a><td><td><td><td><td>
        <tr><td>12-18<td><td><td><td><td><td><td>
        <tr><td>18-21<td><td><td><td><td><td><td><a href="#">Woo</a>
        <tr><td>21-24<td><td><td><td><td><td><a href="#">Baz</a><td>
    </table>
    <button>Next Week</button>
</div>

9.2. Controlling the interaction with scrolling: the spatial-navigation-action property

When the focus is inside of a scroll container and the user triggers spatial navigation, it is somewhat ambiguous whether they are requesting that the focus be moved in that direction, or whether the document should be scrolled in that direction. By default, this is automatically determined, but this property allows the author to decide between focusing or scrolling.

The precise behavior is defined in § 8.3 Navigation, but a high level description of the effect of each value is provided below.

When spatial navigation is triggered, the behavior depends on the value of the spatial-navigation-action on the currently focused element if that element is a scroll container, or of its nearest scroll container ancestor if it isn’t.

auto

If there are visible focusable elements within the scroll container in the direction requested, the closest one becomes focused. Otherwise, the scroll container is scrolled in the direction requested.

focus

The focus is moved to the nearest focusable element within the scroll container, regardless of whether it is visible. If there are none, the scroll container is not scrolled, and the search continues up the ancestry chain instead.

Note: The scroll container may be scrolled as a side effect of focusing an element which was previously not in view, but it will not be directionally scrolled.

Note: If the focus value is given to spatial-navigation-action, navnotarget event occurs when there isn’t any visible candidate in the given direction within the viewport of the spatial navigation container even if the container can be scrolled more.

scroll

If the currently focused element is not itself a scroll container, this value on an ancestor scroll container has the same effect as auto.

If the currently focused element is a scroll container, it is scrolled in the direction requested without changing which element is in focus, regardless of the presence of focusable descendants.

Note: This means that spatial navigation can be used to move the focus to a scroll container and to scroll it, but not to move the focus to its descendants. However, if the focus is moved to a descendant by some other mean (such as pressing the Tab key or using the <focus()> method) spatial navigation can be used to move the focus to other focusable descendants.

Note: The scroll value is at-risk.

Note: Earlier version of this specification did not offer a declarative way to opt into the behavior defined by focus, and instead offered a cancellable event that would be fired before scrolling, so that the author could implement that behavior themselves. However, cancellable events related to scrolling can cause performance problems, so this event was removed and the spatial-navigation-action property was introduced instead.

In this example, a scrollable container is specified with spatial-navigation-action: focus. Inside the container, there is an element which is out of the view within a scrollport. Pressing the down arrow key moves the focus directly to it without scrolling manually.

<div class='scroller'>
    <button class='item'>Box 1</button>
    <button class='item'>Box 2</button>
    <button class='item'>Box 3</button>
</div>

.scroller {
    display: grid;
    grid-template-columns: repeat(1, 1fr);
    height: 300px;
    width: 200px;
    overflow-y: scroll;
    spatial-navigation-action: focus;
}
.item {
    height: 100px;
    width: 100px;
    margin: 50px auto;
    background-color: blue;
}
:focus {
    background-color: red;
}

9.3. Selecting the navigation algorithm: the spatial-navigation-function property

The default algorithm of spatial navigation specified in the § 8 Processing Model may need the fine tune depending on the layout types. This property allows the author to indicate which navigation algorithm is reasonable for spatial navigation behavior.

Its values are defined as follows:

normal

Moves the focus with the default focus navigation algorithm defined by UA.

In general, the focus moves to the element with the closest distance calculated by finding the shortest distance.

grid

Moves the focus to the element which is aligned most in the navigation direction.

• If there are more than one aligned candidates in the navigation direction, select the element with the closest distance along the axis which corresponds to the navigation direction. In case of multiple elements with the same distance, select the element with the minimum amount of alignment.

• Else if there isn’t any aligned candidate in a given direction, select the element with the closest distance along the axis which corresponds to the navigation direction. In case of multiple elements with the same distance, select the element with the minimum distance along the axis which is orthogonal to the navigation direction.

NOTE: These values are negotiated with the users' preferences which seems natural spatial navigation behavior for their pages.

This example shows how the focus moves differently by the value of spatial-navigation-function.

Let the element which contains "A", "B" and "C" is the spatial navigation container.

When the user presses the down arrow key, if normal value is given to spatial-navigation-function of the element, the focus will move to "B". Otherwise, grid value was specified to the element, the focus will move to "C".

Appendix A. Scroll extensions

This section proposes a few extensions to CSS that should be integrated in upstream specifications, but are hosted here until then.

Appendix B. Privacy and Security Considerations

The specification contributors believe that all known potential security risks associated with this specification have been adequately addressed. Further details are provided below.

The TAG has developed a self-review questionnaire to help editors and Working Groups evaluate the risks introduced by their specifications. Answers are provided below.

Does this specification deal with personally-identifiable information?

No.

Does this specification deal with high-value data?

No.

Does this specification introduce new state for an origin that persists across browsing sessions?

No.

Does this specification expose persistent, cross-origin state to the web?

No.

Does this specification expose any other data to an origin that it doesn’t currently have access to?

Mostly, no.

The one exception identified would be in the following scenario: if the author uses `window.navigate` while the focus is in a cross origin iframe, if they don’t get an event at all it means that either there was something scrollable or focusable within the iframe, as the only case where they’d get an event is when the search didn’t find anything at all goes up the tree.

This is so limited information that it does not seem it would introduces real a security risk, but it is as far as the editors can tell information that the author could not get could not get otherwise.

Does this specification enable new script execution/loading mechanisms?

No.

Does this specification allow an origin access to a user’s location?

No.

Does this specification allow an origin access to sensors on a user’s device?

No.

Does this specification allow an origin access to aspects of a user’s local computing environment?

No.

Does this specification allow an origin access to other devices?

No.

Does this specification allow an origin some measure of control over a user agent’s native UI?

No control is given over the appearance of the user agent’s UI. Some control is given over how the user agent performs spatial navigation, which may be considered part of its user interface. This is intentional, to let the author tailor the behavior of spatial navigation to their pages. To prevent malicious the author to interfere with the users' desire to control focus and navigate the document, this overriding mechanism is disabled by default for cross-origin iframes. See § 7 The navigation-override policy-controlled feature.

Does this specification expose temporary identifiers to the web?

No.

Does this specification distinguish between behavior in first-party and third-party contexts?

No.

How should this specification work in the context of a user agent’s "incognito" mode?

No Difference.

Does this specification persist data to a user’s local device?

No.

Does this specification have a "Security Considerations" and "Privacy Considerations" section?

Yes, this is the section you are reading now.

Does this specification allow downgrading default security characteristics?

It does not allow downgrading any unrelated security mechanism.

It **does** allow the author to opt into allowing the events needed to override the default behavior of spatial navigation in cross origin iframes they trust using [feature-policy]. See § 7 The navigation-override policy-controlled feature.

Acknowledgements

The editors of this specification would like to thank the following individuals for their feedback and contributions (in alphabetical order):

• Alice Boxhall

• Brian Kardell

• Elika Etemad

• Eric Seong

• Hugo Holgersson

• Hyojin Song

• Jeonghee Ahn

• Junho Seo

• Rob Dodson

• Seungcheon Baek

Changes

This section is non-normative.

The following changes were made since the 23 April 2019 First Public Working Draft.

• Changed the result of getSpatialNavigationContainer() to return the nearest spatial navigation container ancestor

• Added spatial-navigation-function

• Added updating the search origin step

• Changed the IDL of spatialNavigationSearch() as separating the dir attribute from SpatialNavigationSearchOptions

• Made the focusable element fully overlapped with search origin which is not the spatial navigation container as a candidate for fixing the unreachability