HTML

Living Standard — Last Updated 16 January 2024

1. 6 User interaction
   1. 6.1 The hidden attribute
   2. 6.2 Page visibility
      1. 6.2.1 The VisibilityStateEntry interface
   3. 6.3 Inert subtrees
      1. 6.3.1 Modal dialogs and inert subtrees
      2. 6.3.2 The inert attribute
   4. 6.4 Tracking user activation
      1. 6.4.1 Data model
      2. 6.4.2 Processing model
      3. 6.4.3 APIs gated by user activation
      4. 6.4.4 The UserActivation interface
      5. 6.4.5 User agent automation
   5. 6.5 Activation behavior of elements
      1. 6.5.1 The ToggleEvent interface
   6. 6.6 Focus
      1. 6.6.1 Introduction
      2. 6.6.2 Data model
      3. 6.6.3 The tabindex attribute
      4. 6.6.4 Processing model
      5. 6.6.5 Sequential focus navigation
      6. 6.6.6 Focus management APIs
      7. 6.6.7 The autofocus attribute
   7. 6.7 Assigning keyboard shortcuts
      1. 6.7.1 Introduction
      2. 6.7.2 The accesskey attribute
      3. 6.7.3 Processing model
   8. 6.8 Editing
      1. 6.8.1 Making document regions editable: The contenteditable content attribute
      2. 6.8.2 Making entire documents editable: the designMode getter and setter
      3. 6.8.3 Best practices for in-page editors
      4. 6.8.4 Editing APIs
      5. 6.8.5 Spelling and grammar checking
      6. 6.8.6 Autocapitalization
      7. 6.8.7 Input modalities: the inputmode attribute
      8. 6.8.8 Input modalities: the enterkeyhint attribute
   9. 6.9 Find-in-page
      1. 6.9.1 Introduction
      2. 6.9.2 Interaction with details and hidden=until-found
      3. 6.9.3 Interaction with selection
   10. 6.10 Close requests and close watchers
       1. 6.10.1 Close requests
       2. 6.10.2 Close watcher infrastructure
       3. 6.10.3 The CloseWatcher interface

6 User interaction

6.1 The hidden attribute

All HTML elements may have the hidden content attribute set. The hidden attribute is an enumerated attribute with the following keywords and states:

The attribute's missing value default is the not hidden state, and its invalid value default is the hidden state.

When an element has the hidden attribute in the hidden state, it indicates that the element is not yet, or is no longer, directly relevant to the page's current state, or that it is being used to declare content to be reused by other parts of the page as opposed to being directly accessed by the user. User agents should not render elements that are in the hidden state. This requirement may be implemented indirectly through the style layer. For example, a web browser could implement these requirements using the rules suggested in the Rendering section.

When an element has the hidden attribute in the hidden until found state, it indicates that the element is hidden like the hidden state but the content inside the element will be accessible to find-in-page and fragment navigation. When these features attempt to scroll to a target which is in the element's subtree, the user agent will remove the hidden attribute in order to reveal the content before scrolling to it. In addition to removing the hidden attribute, an event named beforematch is also fired on the element before the hidden attribute is removed.

Web browsers will use 'content-visibility: hidden' instead of 'display: none' when the hidden attribute is in the hidden until found state, as specified in the Rendering section.

  <h1>The Example Game</h1>
  <section id="login">
   <h2>Login</h2>
   <form>
    ...
    <!-- calls login() once the user's credentials have been checked -->
   </form>
   <script>
    function login() {
      // switch screens
      document.getElementById('login').hidden = true;
      document.getElementById('game').hidden = false;
    }
   </script>
  </section>
  <section id="game" hidden>
   ...
  </section>

The hidden attribute must not be used to hide content that could legitimately be shown in another presentation. For example, it is incorrect to use hidden to hide panels in a tabbed dialog, because the tabbed interface is merely a kind of overflow presentation — one could equally well just show all the form controls in one big page with a scrollbar. It is similarly incorrect to use this attribute to hide content just from one presentation — if something is marked hidden, it is hidden from all presentations, including, for instance, screen readers.

Elements that are not themselves hidden must not hyperlink to elements that are hidden. The for attributes of label and output elements that are not themselves hidden must similarly not refer to elements that are hidden. In both cases, such references would cause user confusion.

Elements and scripts may, however, refer to elements that are hidden in other contexts.

Elements in a section hidden by the hidden attribute are still active, e.g. scripts and form controls in such sections still execute and submit respectively. Only their presentation to the user changes.

The hidden getter steps are:

1. If the hidden attribute is in the hidden until found state, then return "until-found".

2. If the hidden attribute is set, then return true.

3. Return false.

The hidden setter steps are:

1. If the given value is a string that is an ASCII case-insensitive match for "until-found", then set the hidden attribute to "until-found".

2. Otherwise, if the given value is false, then remove the hidden attribute.

3. Otherwise, if the given value is the empty string, then remove the hidden attribute.

4. Otherwise, if the given value is null, then remove the hidden attribute.

5. Otherwise, if the given value is 0, then remove the hidden attribute.

6. Otherwise, if the given value is NaN, then remove the hidden attribute.

7. Otherwise, set the hidden attribute to the empty string.

The ancestor hidden-until-found revealing algorithm is to run the following steps on currentNode:

1. While currentNode has a parent node within the flat tree:

   1. If currentNode has the hidden attribute in the hidden until found state, then:

      1. Fire an event named beforematch at currentNode.

      2. Remove the hidden attribute from currentNode.

   2. Set currentNode to the parent node of currentNode within the flat tree.

6.2 Page visibility

A traversable navigable's system visibility state, including its initial value upon creation, is determined by the user agent. It represents, for example, whether the browser window is minimized, a browser tab is currently in the background, or a system element such as a task switcher obscures the page.

When a user-agent determines that the system visibility state for traversable navigable traversable has changed to newState, it must run the following steps:

1. Let navigables be the inclusive descendant navigables of traversable's active document.

2. For each navigable of navigables in what order?:

   1. Let document be navigable's active document.

   2. Queue a global task on the user interaction task source given document's relevant global object to update the visibility state of document with newState.

A Document has a visibility state, which is either "hidden" or "visible", initially set to "hidden".

The visibilityState getter steps are to return this's visibility state.

The hidden getter steps are to return true if this's visibility state is "hidden", otherwise false.

To update the visibility state of Document document to visibilityState:

1. If document's visibility state equals visibilityState, then return.

2. Set document's visibility state to visibilityState.

3. Queue a new VisibilityStateEntry whose visibility state is visibilityState and whose timestamp is the current high resolution time given document's relevant global object.

4. Run the screen orientation change steps with document. [SCREENORIENTATION]

5. Run any page visibility change steps which may be defined in other specifications, with visibility state and document.

   It would be better if specification authors sent a pull request to add calls from here into their specifications directly, instead of using the page visibility change steps hook, to ensure well-defined cross-specification call order. As of the time of this writing the following specifications are known to have page visibility change steps, which will be run in an unspecified order: Device Posture API and Web NFC. [DEVICEPOSTURE] [WEBNFC]

6. Fire an event named visibilitychange at document, with its bubbles attribute initialized to true.

6.2.1 The VisibilityStateEntry interface

The VisibilityStateEntry interface exposes visibility changes to the document, from the moment the document becomes active.

function wasHiddenBeforeFirstContentfulPaint() {
    const fcpEntry = performance.getEntriesByName("first-contentful-paint")[0];
    const visibilityStateEntries = performance.getEntriesByType("visibility-state");
    return visibilityStateEntries.some(e =>
                                            e.startTime < fcpEntry.startTime &&
                                            e.name === "hidden");
}

Since hiding a page can cause throttling of rendering and other user-agent operations, it is common to use visibility changes as an indication that such throttling has occurred. However, other things could also cause throttling in different browsers, such as long periods of inactivity.

[Exposed=(Window)]
interface VisibilityStateEntry : PerformanceEntry {
  readonly attribute DOMString name;                 // shadows inherited name
  readonly attribute DOMString entryType;            // shadows inherited entryType
  readonly attribute DOMHighResTimeStamp startTime;  // shadows inherited startTime
  readonly attribute unsigned long duration;         // shadows inherited duration
};

The VisibilityStateEntry has an associated DOMHighResTimeStamp timestamp.

The VisibilityStateEntry has an associated "visible" or "hidden" visibility state.

The name getter steps are to return this's visibility state.

The entryType getter steps are to return "visibility-state".

The startTime getter steps are to return this's timestamp.

The duration getter steps are to return zero.

6.3 Inert subtrees

See also inert for an explanation of the attribute of the same name.

A node (in particular elements and text nodes) can be inert. When a node is inert:

• Hit-testing must act as if the 'pointer-events' CSS property were set to 'none'.

• Text selection functionality must act as if the 'user-select' CSS property were set to 'none'.

• If it is editable, the node behaves as if it were non-editable.

• The user agent should ignore the node for the purposes of find-in-page.

Inert nodes generally cannot be focused, and user agents do not expose the inert nodes to accessibility APIs or assistive technologies. Inert nodes that are commands will become inoperable to users, in the manner described above.

User agents may allow the user to override the restrictions on find-in-page and text selection, however.

By default, a node is not inert.

6.3.1 Modal dialogs and inert subtrees

A Document document is blocked by a modal dialog subject if subject is the topmost dialog element in document's top layer. While document is so blocked, every node that is connected to document, with the exception of the subject element and its flat tree descendants, must become inert.

subject can additionally become inert via the inert attribute, but only if specified on subject itself (i.e., subject escapes inertness of ancestors); subject's flat tree descendants can become inert in a similar fashion.

The dialog element's showModal() method causes this mechanism to trigger, by adding the dialog element to its node document's top layer.

6.3.2 The inert attribute

The inert attribute is a boolean attribute that indicates, by its presence, that the element and all its flat tree descendants which don't otherwise escape inertness (such as modal dialogs) are to be made inert by the user agent.

An inert subtree should not contain any content or controls which are critical to understanding or using aspects of the page which are not in the inert state. Content in an inert subtree will not be perceivable by all users, or interactive. Authors should not specify elements as inert unless the content they represent are also visually obscured in some way. In most cases, authors should not specify the inert attribute on individual form controls. In these instances, the disabled attribute is probably more appropriate.

The following example shows how to mark partially loaded content, visually obscured by a "loading" message, as inert.

<section aria-labelledby=s1>
  <h3 id=s1>Population by City</h3>
  <div class=container>
    <div class=loading><p>Loading...</p></div>
    <div inert>
      <form>
        <fieldset>
          <legend>Date range</legend>
          <div>
            <label for=start>Start</label>
            <input type=date id=start>
          </div>
          <div>
            <label for=end>End</label>
            <input type=date id=end>
          </div>
          <div>
            <button>Apply</button>
          </div>
        </fieldset>
      </form>
      <table>
        <caption>From 20-- to 20--</caption>
        <thead>
          <tr>
            <th>City</th>
            <th>State</th>
            <th>20-- Population</th>
            <th>20-- Population</th>
            <th>Percentage change</th>
          </tr>
        </thead>
        <tbody>
          <!-- ... -->
        </tbody>
      </table>
    </div>
  </div>
</section>

The "loading" overlay obscures the inert content, making it visually apparent that the inert content is not presently accessible. Notice that the heading and "loading" text are not descendants of the element with the inert attribute. This will ensure this text is accessible to all users, while the inert content cannot be interacted with by anyone.

The inert IDL attribute must reflect the content attribute of the same name.

6.4 Tracking user activation

To prevent abuse of certain APIs that could be annoying to users (e.g., opening popups or vibrating phones), user agents allow these APIs only when the user is actively interacting with the web page or has interacted with the page at least once. This "active interaction" state is maintained through the mechanisms defined in this section.

6.4.1 Data model

For the purpose of tracking user activation, each Window W has two relevant values:

• A last activation timestamp, which is either a DOMHighResTimeStamp, positive infinity (indicating that W has never been activated), or negative infinity (indicating that the activation has been consumed). Initially positive infinity.

• A last history-action activation timestamp, which is either a DOMHighResTimeStamp or positive infinity, initially positive infinity.

A user agent also defines a transient activation duration, which is a constant number indicating how long a user activation is available for certain user activation-gated APIs (e.g., for opening popups).

The transient activation duration is expected be at most a few seconds, so that the user can possibly perceive the link between an interaction with the page and the page calling the activation-gated API.

We then have the following boolean user activation states for W:

Sticky activation

When the current high resolution time given W is greater than or equal to the last activation timestamp in W, W is said to have sticky activation.

This is W's historical activation state, indicating whether the user has ever interacted in W. It starts false, then changes to true (and never changes back to false) when W gets the very first activation notification.

Transient activation

When the current high resolution time given W is greater than or equal to the last activation timestamp in W, and less than the last activation timestamp in W plus the transient activation duration, then W is said to have transient activation.

This is W's current activation state, indicating whether the user has interacted in W recently. This starts with a false value, and remains true for a limited time after every activation notification W gets.

The transient activation state is considered expired if it becomes false because the transient activation duration time has elapsed since the last user activation. Note that it can become false even before the expiry time through an activation consumption.

History-action activation

When the last history-action activation timestamp of W is not equal to the last activation timestamp of W, then W is said to have history-action activation.

This is a special variant of user activation, used to allow access to certain session history APIs which, if used too frequently, would make it harder for the user to traverse back using browser UI. It starts with a false value, and becomes true whenever the user interacts with W, but is reset to false through history-action activation consumption. This ensures such APIs cannot be used multiple times in a row without an intervening user activation. But unlike transient activation, there is no time limit within which such APIs must be used.

The last activation timestamp and last history-action activation timestamp are retained even after the Document changes its fully active status (e.g., after navigating away from a Document, or navigating to a cached Document). This means sticky activation state spans multiple navigations as long as the same Document gets reused. For the transient activation state, the original expiry time remains unchanged (i.e., the state still expires within the transient activation duration limit from the original activation triggering input event). It is important to consider this when deciding whether to base certain things off sticky activation or transient activation.

6.4.2 Processing model

When a user interaction causes firing of an activation triggering input event in a Document document, the user agent must perform the following activation notification steps before dispatching the event:

1. Assert: document is fully active.

2. Let windows be « document's relevant global object ».

3. Extend windows with the active window of each of document's ancestor navigables.

4. Extend windows with the active window of each of document's descendant navigables, filtered to include only those navigables whose active document's origin is same origin with document's origin.

5. For each window in windows, set window's last activation timestamp to the current high resolution time.

An activation triggering input event is any event whose isTrusted attribute is true and whose type is one of:

• "keydown", provided the key is neither the Esc key nor a shortcut key reserved by the user agent.
• "mousedown".
• "pointerdown", provided the event's pointerType is "mouse".
• "pointerup", provided the event's pointerType is not "mouse".
• "touchend".

Activation consuming APIs defined in this and other specifications can consume user activation by performing the following steps, given a Window W:

1. If W's navigable is null, then return.

2. Let top be W's navigable's top-level traversable.

3. Let navigables be the inclusive descendant navigables of top's active document.

4. Let windows be the list of Window objects constructed by taking the active window of each item in navigables.

5. For each window in windows, if window's last activation timestamp is not positive infinity, then set window's last activation timestamp to negative infinity.

History-action activation-consuming APIs can consume history-action user activation by performing the following steps, given a Window W:

1. If W's navigable is null, then return.

2. Let top be W's navigable's top-level traversable.

3. Let navigables be the inclusive descendant navigables of top's active document.

4. Let windows be the list of Window objects constructed by taking the active window of each item in navigables.

5. For each window in windows, set window's last history-action activation timestamp to window's last activation timestamp.

Note the asymmetry in the sets of browsing contexts in the page that are affected by an activation notification vs an activation consumption: an activation consumption changes (to false) the transient activation states for all browsing contexts in the page, but an activation notification changes (to true) the states for a subset of those browsing contexts. The exhaustive nature of consumption here is deliberate: it prevents malicious sites from making multiple calls to an activation consuming API from a single user activation (possibly by exploiting a deep hierarchy of iframes).

6.4.3 APIs gated by user activation

APIs that are dependent on user activation are classified into different levels:

Sticky activation-gated APIs

These APIs require the sticky activation state to be true, so they are blocked until the very first user activation.

Transient activation-gated APIs

These APIs require the transient activation state to be true, but they don't consume it, so multiple calls are allowed per user activation until the transient state expires.

Transient activation-consuming APIs

These APIs require the transient activation state to be true, and they consume user activation in each call to prevent multiple calls per user activation.

History-action activation-consuming APIs

These APIs require the history-action activation state to be true, and they consume history-action user activation in each call to prevent multiple calls per user activation.

6.4.4 The UserActivation interface

Each Window has an associated UserActivation, which is a UserActivation object. Upon creation of the Window object, its associated UserActivation must be set to a new UserActivation object created in the Window object's relevant realm.

[Exposed=Window]
interface UserActivation {
  readonly attribute boolean hasBeenActive;
  readonly attribute boolean isActive;
};

partial interface Navigator {
  [SameObject] readonly attribute UserActivation userActivation;
};

navigator.userActivation.hasBeenActive

Returns whether the window has sticky activation.

navigator.userActivation.isActive

Returns whether the window has transient activation.

The userActivation getter steps are to return this's relevant global object's associated UserActivation.

The hasBeenActive getter steps are to return true if this's relevant global object has sticky activation, and false otherwise.

The isActive getter steps are to return true if this's relevant global object has transient activation, and false otherwise.

6.4.5 User agent automation

For the purposes of user-agent automation and application testing, this specification defines the following extension command for the Web Driver specification. It is optional for a user agent to support the following extension command. [WEBDRIVER]

The remote end steps are:

1. Let window be current browsing context's active window.

2. Let consume be true if window has transient activation; otherwise false.

3. If consume is true, then consume user activation of window.

4. Return success with data consume.

6.5 Activation behavior of elements

Certain elements in HTML have an activation behavior, which means that the user can activate them. This is always caused by a click event.

The user agent should allow the user to manually trigger elements that have an activation behavior, for instance using keyboard or voice input, or through mouse clicks. When the user triggers an element with a defined activation behavior in a manner other than clicking it, the default action of the interaction event must be to fire a click event at the element.

element.click()

✔MDN

HTMLElement/click

Support in all current engines.

Firefox3+Safari6+Chrome9+

---

Opera10.5+Edge79+

---

Edge (Legacy)12+Internet Explorer5.5+

---

Firefox Android4+Safari iOS?Chrome Android?WebView Android4.4+Samsung Internet1.0+Opera Android11+

Acts as if the element was clicked.

Each element has an associated click in progress flag, which is initially unset.

The click() method must run the following steps:

1. If this element is a form control that is disabled, then return.

2. If this element's click in progress flag is set, then return.

3. Set this element's click in progress flag.

4. Fire a synthetic pointer event named click at this element, with the not trusted flag set.

5. Unset this element's click in progress flag.

6.5.1 The ToggleEvent interface

[Exposed=Window]
interface ToggleEvent : Event {
  constructor(DOMString type, optional ToggleEventInit eventInitDict = {});
  readonly attribute DOMString oldState;
  readonly attribute DOMString newState;
};

dictionary ToggleEventInit : EventInit {
  DOMString oldState = "";
  DOMString newState = "";
};

event.oldState

Set to "closed" when transitioning from closed to open, or set to "open" when transitioning from open to closed.

event.newState

Set to "open" when transitioning from closed to open, or set to "closed" when transitioning from open to closed.

The oldState and newState attributes must return the values they are initialized to.

A toggle task tracker is a struct which has:

task

A task which fires a ToggleEvent.

old state

A string which represents the task's event's value for the oldState attribute.

6.6 Focus

6.6.1 Introduction

This section is non-normative.

An HTML user interface typically consists of multiple interactive widgets, such as form controls, scrollable regions, links, dialog boxes, browser tabs, and so forth. These widgets form a hierarchy, with some (e.g. browser tabs, dialog boxes) containing others (e.g. links, form controls).

When interacting with an interface using a keyboard, key input is channeled from the system, through the hierarchy of interactive widgets, to an active widget, which is said to be focused.

Keyboard events are always targeted at this focused element.

6.6.2 Data model

A top-level traversable has system focus when it can receive keyboard input channeled from the operating system, possibly targeted at one of its active document's descendant navigables.

A top-level traversable has user attention when its system visibility state is "visible", and it either has system focus or user agent widgets directly related to it can receive keyboard input channeled from the operating system.

User attention is lost when a browser window loses focus, whereas system focus might also be lost to other system widgets in the browser window such as a location bar.

A Document d is a fully active descendant of a top-level traversable with user attention when d is fully active and d's node navigable's top-level traversable has user attention.

The term focusable area is used to refer to regions of the interface that can further become the target of such keyboard input. Focusable areas can be elements, parts of elements, or other regions managed by the user agent.

Each focusable area has a DOM anchor, which is a Node object that represents the position of the focusable area in the DOM. (When the focusable area is itself a Node, it is its own DOM anchor.) The DOM anchor is used in some APIs as a substitute for the focusable area when there is no other DOM object to represent the focusable area.

The following table describes what objects can be focusable areas. The cells in the left column describe objects that can be focusable areas; the cells in the right column describe the DOM anchors for those elements. (The cells that span both columns are non-normative examples.)

<map id=wallmap><area alt="Enter Door" coords="10,10,100,200" href="door.html"></map>
...
<img src="images/innerwall.jpeg" alt="There is a white wall here, with a door." usemap="#wallmap">
...
<img src="images/outerwall.jpeg" alt="There is a red wall here, with a door." usemap="#wallmap">

A navigable container (e.g. an iframe) is a focusable area, but key events routed to a navigable container get immediately routed to its content navigable's active document. Similarly, in sequential focus navigation a navigable container essentially acts merely as a placeholder for its content navigable's active document.

One focusable area in each Document is designated the focused area of the document. Which control is so designated changes over time, based on algorithms in this specification.

Even if a document is not fully active and not shown to the user, it can still have a focused area of the document. If a document's fully active state changes, its focused area of the document will stay the same.

The currently focused area of a top-level traversable traversable is the focusable area-or-null returned by this algorithm:

1. If traversable does not have system focus, then return null.

2. Let candidate be traversable's active document.

3. While candidate's focused area is a navigable container with a non-null content navigable: set candidate to the active document of that navigable container's content navigable.

4. If candidate's focused area is non-null, set candidate to candidate's focused area.

5. Return candidate.

The current focus chain of a top-level traversable traversable is the focus chain of the currently focused area of traversable, if traversable is non-null, or an empty list otherwise.

An element that is the DOM anchor of a focusable area is said to gain focus when that focusable area becomes the currently focused area of a top-level traversable. When an element is the DOM anchor of a focusable area of the currently focused area of a top-level traversable, it is focused.

The focus chain of a focusable area subject is the ordered list constructed as follows:

1. Let output be an empty list.

2. Let currentObject be subject.

3. While true:

   1. Append currentObject to output.

   2. If currentObject is an area element's shape, then append that area element to output.

      Otherwise, if currentObject's DOM anchor is an element that is not currentObject itself, then append currentObject's DOM anchor to output.

   3. If currentObject is a focusable area, then set currentObject to currentObject's DOM anchor's node document.

      Otherwise, if currentObject is a Document whose node navigable's parent is non-null, then set currentObject to currentObject's node navigable's parent.

      Otherwise, break.

4. Return output.

   The chain starts with subject and (if subject is or can be the currently focused area of a top-level traversable) continues up the focus hierarchy up to the Document of the top-level traversable.

All elements that are focusable areas are said to be focusable.

There are two special types of focusability for focusable areas:

• A focusable area is said to be sequentially focusable if it is included in its Document's sequential focus navigation order and the user agent determines that it is sequentially focusable.

• A focusable area is said to be click focusable if the user agent determines that it is click focusable. User agents should consider focusable areas with non-null tabindex values to be click focusable.

Elements which are not focusable are not focusable areas, and thus not sequentially focusable and not click focusable.

When a user activates a click focusable focusable area, the user agent must run the focusing steps on the focusable area with focus trigger set to "click".

Note that focusing is not an activation behavior, i.e. calling the click() method on an element or dispatching a synthetic click event on it won't cause the element to get focused.

A node is a focus navigation scope owner if it is a Document, a shadow host, a slot, or an element in the popover showing state which also has a popover invoker set.

Each focus navigation scope owner has a focus navigation scope, which is a list of elements. Its contents are determined as follows:

Every element element has an associated focus navigation owner, which is either null or a focus navigation scope owner. It is determined by the following algorithm:

1. If element's parent is null, then return null.

2. If element's parent is a shadow host, then return element's assigned slot.

3. If element's parent is a shadow root, then return the parent's host.

4. If element's parent is the document element, then return the parent's node document.

5. If element is in the popover showing state and has a popover invoker set, then return element.

6. Return element's parent's associated focus navigation owner.

Then, the contents of a given focus navigation scope owner owner's focus navigation scope are all elements whose associated focus navigation owner is owner.

The order of elements within a focus navigation scope does not impact any of the algorithms in this specification. Ordering only becomes important for the tabindex-ordered focus navigation scope and flattened tabindex-ordered focus navigation scope concepts defined below.

A tabindex-ordered focus navigation scope is a list of focusable areas and focus navigation scope owners. Every focus navigation scope owner owner has tabindex-ordered focus navigation scope, whose contents are determined as follows:

• It contains all elements in owner's focus navigation scope that are themselves focus navigation scope owners, except the elements whose tabindex value is a negative integer.

• It contains all of the focusable areas whose DOM anchor is an element in owner's focus navigation scope, except the focusable areas whose tabindex value is a negative integer.

The order within a tabindex-ordered focus navigation scope is determined by each element's tabindex value, as described in the section below.

The rules there do not give a precise ordering, as they are composed mostly of "should" statements and relative orderings.

A flattened tabindex-ordered focus navigation scope is a list of focusable areas. Every focus navigation scope owner owner owns a distinct flattened tabindex-ordered focus navigation scope, whose contents are determined by the following algorithm:

1. Let result be a clone of owner's tabindex-ordered focus navigation scope.

2. For each item of result:

   1. If item is not a focus navigation scope owner, then continue.

   2. If item is not a focusable area, then replace item with all of the items in item's flattened tabindex-ordered focus navigation scope.

   3. Otherwise, insert the contents of item's flattened tabindex-ordered focus navigation scope after item.

6.6.3 The tabindex attribute

The tabindex content attribute allows authors to make an element and regions that have the element as its DOM anchor be focusable areas, allow or prevent them from being sequentially focusable, and determine their relative ordering for sequential focus navigation.

The name "tab index" comes from the common use of the Tab key to navigate through the focusable elements. The term "tabbing" refers to moving forward through sequentially focusable focusable areas.

The tabindex attribute, if specified, must have a value that is a valid integer. Positive numbers specify the relative position of the element's focusable areas in the sequential focus navigation order, and negative numbers indicate that the control is not sequentially focusable.

Developers should use caution when using values other than 0 or −1 for their tabindex attributes as this is complicated to do correctly.

The tabindex value of an element is the value of its tabindex attribute, parsed using the rules for parsing integers. If parsing fails or the attribute is not specified, then the tabindex value is null.

The tabindex value of a focusable area is the tabindex value of its DOM anchor.

The tabindex value of an element must be interpreted as follows:

If the value is null

The user agent should follow platform conventions to determine if the element should be considered as a focusable area and if so, whether the element and any focusable areas that have the element as their DOM anchor are sequentially focusable, and if so, what their relative position in their tabindex-ordered focus navigation scope is to be. If the element is a focus navigation scope owner, it must be included in its tabindex-ordered focus navigation scope even if it is not a focusable area.

The relative ordering within a tabindex-ordered focus navigation scope for elements and focusable areas that belong to the same focus navigation scope and whose tabindex value is null should be in shadow-including tree order.

Modulo platform conventions, it is suggested that the following elements should be considered as focusable areas and be sequentially focusable:

• a elements that have an href attribute
• button elements
• input elements whose type attribute are not in the Hidden state
• select elements
• textarea elements
• summary elements that are the first summary element child of a details element
• Elements with a draggable attribute set, if that would enable the user agent to allow the user to begin drag operations for those elements without the use of a pointing device
• Editing hosts
• Navigable containers

If the value is a negative integer

The user agent must consider the element as a focusable area, but should omit the element from any tabindex-ordered focus navigation scope.

One valid reason to ignore the requirement that sequential focus navigation not allow the author to lead to the element would be if the user's only mechanism for moving the focus is sequential focus navigation. For instance, a keyboard-only user would be unable to click on a text control with a negative tabindex, so that user's user agent would be well justified in allowing the user to tab to the control regardless.

If the value is a zero

The user agent must allow the element to be considered as a focusable area and should allow the element and any focusable areas that have the element as their DOM anchor to be sequentially focusable.

The relative ordering within a tabindex-ordered focus navigation scope for elements and focusable areas that belong to the same focus navigation scope and whose tabindex value is zero should be in shadow-including tree order.

If the value is greater than zero

The user agent must allow the element to be considered as a focusable area and should allow the element and any focusable areas that have the element as their DOM anchor to be sequentially focusable, and should place the element — referenced as candidate below — and the aforementioned focusable areas in the tabindex-ordered focus navigation scope where the element is a part of so that, relative to other elements and focusable areas that belong to the same focus navigation scope, they are:

• before any focusable area whose DOM anchor is an element whose tabindex attribute has been omitted or whose value, when parsed, returns an error,
• before any focusable area whose DOM anchor is an element whose tabindex attribute has a value equal to or less than zero,
• after any focusable area whose DOM anchor is an element whose tabindex attribute has a value greater than zero but less than the value of the tabindex attribute on candidate,
• after any focusable area whose DOM anchor is an element whose tabindex attribute has a value equal to the value of the tabindex attribute on candidate but that is located earlier than candidate in shadow-including tree order,
• before any focusable area whose DOM anchor is an element whose tabindex attribute has a value equal to the value of the tabindex attribute on candidate but that is located later than candidate in shadow-including tree order, and
• before any focusable area whose DOM anchor is an element whose tabindex attribute has a value greater than the value of the tabindex attribute on candidate.

The tabIndex IDL attribute must reflect the value of the tabindex content attribute. The default value is 0 if the element is an a, area, button, frame, iframe, input, object, select, textarea, or SVG a element, or is a summary element that is a summary for its parent details. The default value is −1 otherwise.

The varying default value based on element type is a historical artifact.

6.6.4 Processing model

To get the focusable area for a focus target that is either an element that is not a focusable area, or is a navigable, given an optional string focus trigger (default "other"), run the first matching set of steps from the following list:

If focus target is an area element with one or more shapes that are focusable areas

Return the shape corresponding to the first img element in tree order that uses the image map to which the area element belongs.

If focus target is an element with one or more scrollable regions that are focusable areas

Return the element's first scrollable region, according to a pre-order, depth-first traversal of the flat tree. [CSSSCOPING]

If focus target is the document element of its Document

Return the Document's viewport.

If focus target is a navigable

Return the navigable's active document.

If focus target is a navigable container with a non-null content navigable

Return the navigable container's content navigable's active document.

If focus target is a shadow host whose shadow root's delegates focus is true

1. Let focusedElement be the currently focused area of a top-level traversable's DOM anchor.

2. If focus target is a shadow-including inclusive ancestor of focusedElement, then return focusedElement.

3. Return the focus delegate for focus target given focus trigger.

For sequential focusability, the handling of shadow hosts and delegates focus is done when constructing the sequential focus navigation order. That is, the focusing steps will never be called on such shadow hosts as part of sequential focus navigation.

Otherwise

Return null.

The focus delegate for a focusTarget, given an optional string focusTrigger (default "other"), is given by the following steps:

1. If focusTarget is a shadow host and its shadow root's delegates focus is false, then return null.

2. Let whereToLook be focusTarget.

3. If whereToLook is a shadow host, then set whereToLook to whereToLook's shadow root.

4. Let autofocusDelegate be the autofocus delegate for whereToLook given focusTrigger.

5. If autofocusDelegate is not null, then return autofocusDelegate.

6. For each descendant of whereToLook's descendants, in tree order:

   1. Let focusableArea be null.

   2. If focusTarget is a dialog element and descendant is sequentially focusable, then set focusableArea to descendant.

   3. Otherwise, if focusTarget is not a dialog and descendant is a focusable area, set focusableArea to descendant.

   4. Otherwise, set focusableArea to the result of getting the focusable area for descendant given focusTrigger.

      This step can end up recursing, i.e., the get the focusable area steps might return the focus delegate of descendant.

   5. If focusableArea is not null, then return focusableArea.

   It's important that we are not looking at the shadow-including descendants here, but instead only at the descendants. Shadow hosts are instead handled by the recursive case mentioned above.

7. Return null.

The above algorithm essentially returns the first suitable focusable area where the path between its DOM anchor and focusTarget delegates focus at any shadow tree boundaries.

The autofocus delegate for a focus target given a focus trigger is given by the following steps:

1. For each descendant descendant of focus target, in tree order:

   1. If descendant does not have an autofocus content attribute, then continue.

   2. Let focusable area be descendant, if descendant is a focusable area; otherwise let focusable area be the result of getting the focusable area for descendant given focus trigger.

   3. If focusable area is null, then continue.

   4. If focusable area is not click focusable and focus trigger is "click", then continue.

   5. Return focusable area.

2. Return null.

The focusing steps for an object new focus target that is either a focusable area, or an element that is not a focusable area, or a navigable, are as follows. They can optionally be run with a fallback target and a string focus trigger.

1. If new focus target is not a focusable area, then set new focus target to the result of getting the focusable area for new focus target, given focus trigger if it was passed.

2. If new focus target is null, then:

   1. If no fallback target was specified, then return.

   2. Otherwise, set new focus target to the fallback target.

3. If new focus target is a navigable container with non-null content navigable, then set new focus target to the content navigable's active document.

4. If new focus target is a focusable area and its DOM anchor is inert, then return.

5. If new focus target is the currently focused area of a top-level traversable, then return.

6. Let old chain be the current focus chain of the top-level traversable in which new focus target finds itself.

7. Let new chain be the focus chain of new focus target.

8. Run the focus update steps with old chain, new chain, and new focus target respectively.

User agents must immediately run the focusing steps for a focusable area or navigable candidate whenever the user attempts to move the focus to candidate.

The unfocusing steps for an object old focus target that is either a focusable area or an element that is not a focusable area are as follows:

1. If old focus target is a shadow host whose shadow root's delegates focus is true, and old focus target's shadow root is a shadow-including inclusive ancestor of the currently focused area of a top-level traversable's DOM anchor, then set old focus target to that currently focused area of a top-level traversable.

2. If old focus target is inert, then return.

3. If old focus target is an area element and one of its shapes is the currently focused area of a top-level traversable, or, if old focus target is an element with one or more scrollable regions, and one of them is the currently focused area of a top-level traversable, then let old focus target be that currently focused area of a top-level traversable.

4. Let old chain be the current focus chain of the top-level traversable in which old focus target finds itself.

5. If old focus target is not one of the entries in old chain, then return.

6. If old focus target is not a focusable area, then return.

7. Let topDocument be old chain's last entry.

8. If topDocument's node navigable has system focus, then run the focusing steps for topDocument's viewport.

   Otherwise, apply any relevant platform-specific conventions for removing system focus from topDocument's node navigable, and run the focus update steps given old chain, an empty list, and null.

The unfocusing steps do not always result in the focus changing, even when applied to the currently focused area of a top-level traversable. For example, if the currently focused area of a top-level traversable is a viewport, then it will usually keep its focus regardless until another focusable area is explicitly focused with the focusing steps.

The focus update steps, given an old chain, a new chain, and a new focus target respectively, are as follows:

1. If the last entry in old chain and the last entry in new chain are the same, pop the last entry from old chain and the last entry from new chain and redo this step.

2. For each entry entry in old chain, in order, run these substeps:

   1. If entry is an input element, and the change event applies to the element, and the element does not have a defined activation behavior, and the user has changed the element's value or its list of selected files while the control was focused without committing that change (such that it is different to what it was when the control was first focused), then:

      1. Set entry's user interacted to true.

      2. Fire an event named change at the element, with the bubbles attribute initialized to true.

   2. If entry is an element, let blur event target be entry.

      If entry is a Document object, let blur event target be that Document object's relevant global object.

      Otherwise, let blur event target be null.

   3. If entry is the last entry in old chain, and entry is an Element, and the last entry in new chain is also an Element, then let related blur target be the last entry in new chain. Otherwise, let related blur target be null.

   4. If blur event target is not null, fire a focus event named blur at blur event target, with related blur target as the related target.

      In some cases, e.g., if entry is an area element's shape, a scrollable region, or a viewport, no event is fired.

3. Apply any relevant platform-specific conventions for focusing new focus target. (For example, some platforms select the contents of a text control when that control is focused.)

4. For each entry entry in new chain, in reverse order, run these substeps:

   1. If entry is a focusable area, and the focused area of the document is not entry:

      1. Set document's relevant global object's navigation API's focus changed during ongoing navigation to true.

      2. Designate entry as the focused area of the document.

   2. If entry is an element, let focus event target be entry.

      If entry is a Document object, let focus event target be that Document object's relevant global object.

      Otherwise, let focus event target be null.

   3. If entry is the last entry in new chain, and entry is an Element, and the last entry in old chain is also an Element, then let related focus target be the last entry in old chain. Otherwise, let related focus target be null.

   4. If focus event target is not null, fire a focus event named focus at focus event target, with related focus target as the related target.

      In some cases, e.g. if entry is an area element's shape, a scrollable region, or a viewport, no event is fired.

To fire a focus event named e at an element t with a given related target r, fire an event named e at t, using FocusEvent, with the relatedTarget attribute initialized to r, the view attribute initialized to t's node document's relevant global object, and the composed flag set.

When a key event is to be routed in a top-level traversable, the user agent must run the following steps:

1. Let target area be the currently focused area of the top-level traversable.

2. Assert: target area is not null, since key events are only routed to top-level traversables that have system focus. Therefore, target area is a focusable area.

3. Let target node be target area's DOM anchor.

4. If target node is a Document that has a body element, then let target node be the body element of that Document.

   Otherwise, if target node is a Document object that has a non-null document element, then let target node be that document element.

5. If target node is not inert, then:

   1. Let canHandle be the result of dispatching the key event at target node.

   2. If canHandle is true, then let target area handle the key event. This might include firing a click event at target node.

The has focus steps, given a Document object target, are as follows:

1. If target's node navigable's top-level traversable does not have system focus, then return false.

2. Let candidate be target's node navigable's top-level traversable's active document.

3. While true:

   1. If candidate is target, then return true.

   2. If the focused area of candidate is a navigable container with a non-null content navigable, then set candidate to the active document of that navigable container's content navigable.

   3. Otherwise, return false.

6.6.5 Sequential focus navigation

Each Document has a sequential focus navigation order, which orders some or all of the focusable areas in the Document relative to each other. Its contents and ordering are given by the flattened tabindex-ordered focus navigation scope of the Document.

Per the rules defining the flattened tabindex-ordered focus navigation scope, the ordering is not necessarily related to the tree order of the Document.

If a focusable area is omitted from the sequential focus navigation order of its Document, then it is unreachable via sequential focus navigation.

There can also be a sequential focus navigation starting point. It is initially unset. The user agent may set it when the user indicates that it should be moved.

For example, the user agent could set it to the position of the user's click if the user clicks on the document contents.

User agents are required to set the sequential focus navigation starting point to the target element when navigating to a fragment.

When the user requests that focus move from the currently focused area of a top-level traversable to the next or previous focusable area (e.g. as the default action of pressing the tab key), or when the user requests that focus sequentially move to a top-level traversable in the first place (e.g. from the browser's location bar), the user agent must use the following algorithm:

1. Let starting point be the currently focused area of a top-level traversable, if the user requested to move focus sequentially from there, or else the top-level traversable itself, if the user instead requested to move focus from outside the top-level traversable.

2. If there is a sequential focus navigation starting point defined and it is inside starting point, then let starting point be the sequential focus navigation starting point instead.

3. Let direction be forward if the user requested the next control, and backward if the user requested the previous control.

   Typically, pressing tab requests the next control, and pressing shift + tab requests the previous control.

4. Loop: Let selection mechanism be sequential if the starting point is a navigable or if starting point is in its Document's sequential focus navigation order.

   Otherwise, starting point is not in its Document's sequential focus navigation order; let selection mechanism be DOM.

5. Let candidate be the result of running the sequential navigation search algorithm with starting point, direction, and selection mechanism as the arguments.

6. If candidate is not null, then run the focusing steps for candidate and return.

7. Otherwise, unset the sequential focus navigation starting point.

8. If starting point is a top-level traversable, or a focusable area in the top-level traversable, the user agent should transfer focus to its own controls appropriately (if any), honouring direction, and then return.

   For example, if direction is backward, then the last sequentially focusable control before the browser's rendering area would be the control to focus.

   If the user agent has no sequentially focusable controls — a kiosk-mode browser, for instance — then the user agent may instead restart these steps with the starting point being the top-level traversable itself.

9. Otherwise, starting point is a focusable area in a child navigable. Set starting point to that child navigable's parent and return to the step labeled loop.

The sequential navigation search algorithm consists of the following steps. This algorithm takes three arguments: starting point, direction, and selection mechanism.

1. Pick the appropriate cell from the following table, and follow the instructions in that cell.

   The appropriate cell is the one that is from the column whose header describes direction and from the first row whose header describes starting point and selection mechanism.

   	direction is forward	direction is backward
   starting point is a navigable	Let candidate be the first suitable sequentially focusable area in starting point's active document, if any; or else null	Let candidate be the last suitable sequentially focusable area in starting point's active document, if any; or else null
   selection mechanism is DOM	Let candidate be the first suitable sequentially focusable area in the home document following starting point, if any; or else null	Let candidate be the last suitable sequentially focusable area in the home document preceding starting point, if any; or else null
   selection mechanism is sequential	Let candidate be the first suitable sequentially focusable area in the home sequential focus navigation order following starting point, if any; or else null	Let candidate be the last suitable sequentially focusable area in the home sequential focus navigation order preceding starting point, if any; or else null

   A suitable sequentially focusable area is a focusable area whose DOM anchor is not inert and is sequentially focusable.

   The home document is the Document to which starting point belongs.

   The home sequential focus navigation order is the sequential focus navigation order to which starting point belongs.

   The home sequential focus navigation order is the home document's sequential focus navigation order, but is only used when the starting point is in that sequential focus navigation order (when it's not, selection mechanism will be DOM).

2. If candidate is a navigable container with a non-null content navigable, then let new candidate be the result of running the sequential navigation search algorithm with candidate's content navigable as the first argument, direction as the second, and sequential as the third.

   If new candidate is null, then let starting point be candidate, and return to the top of this algorithm. Otherwise, let candidate be new candidate.

3. Return candidate.

6.6.6 Focus management APIs

dictionary FocusOptions {
  boolean preventScroll = false;
  boolean focusVisible;
};

documentOrShadowRoot.activeElement

✔MDN

Document/activeElement

Support in all current engines.

Firefox3+Safari4+Chrome2+

---

Opera12.1+Edge79+

---

Edge (Legacy)12+Internet Explorer6+

---

Firefox Android?Safari iOS?Chrome Android?WebView Android37+Samsung Internet?Opera Android12.1+

ShadowRoot/activeElement

Support in all current engines.

Firefox63+Safari10+Chrome53+

---

Opera?Edge79+

---

Edge (Legacy)?Internet ExplorerNo

---

Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

Returns the deepest element in the document through which or to which key events are being routed. This is, roughly speaking, the focused element in the document.

For the purposes of this API, when a child navigable is focused, its container is focused within its parent's active document. For example, if the user moves the focus to a text control in an iframe, the iframe is the element returned by the activeElement API in the iframe's node document.

Similarly, when the focused element is in a different node tree than documentOrShadowRoot, the element returned will be the host that's located in the same node tree as documentOrShadowRoot if documentOrShadowRoot is a shadow-including inclusive ancestor of the focused element, and null if not.

document.hasFocus()

✔MDN

Document/hasFocus

Support in all current engines.

Firefox3+Safari4+Chrome2+

---

Opera?Edge79+

---

Edge (Legacy)12+Internet Explorer5.5+

---

Firefox Android?Safari iOS?Chrome Android?WebView Android37+Samsung Internet?Opera Android?

Returns true if key events are being routed through or to the document; otherwise, returns false. Roughly speaking, this corresponds to the document, or a document nested inside this one, being focused.

window.focus()

✔MDN

Window/focus

Support in all current engines.

Firefox1+Safari1+Chrome1+

---

Opera12.1+Edge79+

---

Edge (Legacy)12+Internet Explorer4+

---

Firefox Android?Safari iOS?Chrome Android18+WebView Android?Samsung Internet?Opera Android12.1+

Moves the focus to the window's navigable, if any.

element.focus([ { preventScroll: true } ])

✔MDN

HTMLElement/focus

Support in all current engines.

Firefox1.5+Safari3+Chrome1+

---

Opera8+Edge79+

---

Edge (Legacy)12+Internet Explorer5.5+

---

Firefox Android?Safari iOS1+Chrome Android?WebView Android?Samsung Internet?Opera Android10.1+

Moves the focus to the element.

If the element is a navigable container, moves the focus to its content navigable instead.

By default, this method also scrolls the element into view. Providing the preventScroll option and setting it to true prevents this behavior.

element.blur()

✔MDN

HTMLElement/blur

Support in all current engines.

Firefox1.5+Safari3+Chrome1+

---

Opera8+Edge79+

---

Edge (Legacy)12+Internet Explorer5.5+

---

Firefox Android?Safari iOS1+Chrome Android?WebView Android?Samsung Internet?Opera Android10.1+

Moves the focus to the viewport. Use of this method is discouraged; if you want to focus the viewport, call the focus() method on the Document's document element.

Do not use this method to hide the focus ring if you find the focus ring unsightly. Instead, use the :focus-visible pseudo-class to override the 'outline' property, and provide a different way to show what element is focused. Be aware that if an alternative focusing style isn't made available, the page will be significantly less usable for people who primarily navigate pages using a keyboard, or those with reduced vision who use focus outlines to help them navigate the page.

For example, to hide the outline from textarea elements and instead use a yellow background to indicate focus, you could use:

textarea:focus-visible { outline: none; background: yellow; color: black; }

The activeElement attribute's getter must run these steps:

1. Let candidate be the DOM anchor of the focused area of this DocumentOrShadowRoot's node document.

2. Set candidate to the result of retargeting candidate against this DocumentOrShadowRoot.

3. If candidate's root is not this DocumentOrShadowRoot, then return null.

4. If candidate is not a Document object, then return candidate.

5. If candidate has a body element, then return that body element.

6. If candidate's document element is non-null, then return that document element.

7. Return null.

The hasFocus() method on the Document object, when invoked, must return the result of running the has focus steps with the Document object as the argument.

The focus() method, when invoked, must run these steps:

1. Let current be this Window object's navigable.

2. If current is null, then return.

3. Run the focusing steps with current.

4. If current is a top-level traversable, user agents are encouraged to trigger some sort of notification to indicate to the user that the page is attempting to gain focus.

The blur() method steps are to do nothing.

Historically, the focus() and blur() methods actually affected the system-level focus of the system widget (e.g., tab or window) that contained the navigable, but hostile sites widely abuse this behavior to the user's detriment.

The focus(options) method on elements, when invoked, must run the following steps:

1. If the element is marked as locked for focus, then return.

2. Mark the element as locked for focus.

3. Run the focusing steps for the element.

4. If the value of the focusVisible dictionary member of options is true, or is not present but in an implementation-defined way the user agent determines it would be best to do so, then indicate focus.

5. If the value of the preventScroll dictionary member of options is false, then scroll the element into view given "auto", "center", and "center".

6. Unmark the element as locked for focus.

The blur() method, when invoked, should run the unfocusing steps for the element on which the method was called. User agents may selectively or uniformly ignore calls to this method for usability reasons.

For example, if the blur() method is unwisely being used to remove the focus ring for aesthetics reasons, the page would become unusable by keyboard users. Ignoring calls to this method would thus allow keyboard users to interact with the page.

6.6.7 The autofocus attribute

The autofocus content attribute allows the author to indicate that an element is to be focused as soon as the page is loaded, allowing the user to just start typing without having to manually focus the main element.

When the autofocus attribute is specified on an element inside dialog elements or HTML elements whose popover attribute is set, then it will be focused when the dialog or popover becomes shown.

The autofocus attribute is a boolean attribute.

To find the nearest ancestor autofocus scoping root element given an Element element:

1. If element is a dialog element, then return element.

2. If element's popover attribute is not in the no popover state, then return element.

3. Let ancestor be element.

4. While ancestor has a parent element:

   1. Set ancestor to ancestor's parent element.

   2. If ancestor is a dialog element, then return ancestor.

   3. If ancestor's popover attribute is not in the no popover state, then return ancestor.

5. Return ancestor.

There must not be two elements with the same nearest ancestor autofocus scoping root element that both have the autofocus attribute specified.

Each Document has an autofocus candidates list, initially empty.

Each Document has an autofocus processed flag boolean, initially false.

When an element with the autofocus attribute specified is inserted into a document, run the following steps:

1. If the user has indicated (for example, by starting to type in a form control) that they do not wish focus to be changed, then optionally return.

2. Let target be the element's node document.

3. If target is not fully active, then return.

4. If target's active sandboxing flag set has the sandboxed automatic features browsing context flag, then return.

5. For each ancestorNavigable of target's ancestor navigables: if ancestorNavigable's active document's origin is not same origin with target's origin, then return.

6. Let topDocument be target's node navigable's top-level traversable's active document.

7. If topDocument's autofocus processed flag is false, then remove the element from topDocument's autofocus candidates, and append the element to topDocument's autofocus candidates.

We do not check if an element is a focusable area before storing it in the autofocus candidates list, because even if it is not a focusable area when it is inserted, it could become one by the time flush autofocus candidates sees it.

To flush autofocus candidates for a document topDocument, run these steps:

1. If topDocument's autofocus processed flag is true, then return.

2. Let candidates be topDocument's autofocus candidates.

3. If candidates is empty, then return.

4. If topDocument's focused area is not topDocument itself, or topDocument has non-null target element, then:

   1. Empty candidates.

   2. Set topDocument's autofocus processed flag to true.

   3. Return.

5. While candidates is not empty:

   1. Let element be candidates[0].

   2. Let doc be element's node document.

   3. If doc is not fully active, then remove element from candidates, and continue.

   4. If doc's node navigable's top-level traversable is not the same as topDocument's node navigable, then remove element from candidates, and continue.

   5. If doc's script-blocking style sheet set is not empty, then return.

      In this case, element is the currently-best candidate, but doc is not ready for autofocusing. We'll try again next time flush autofocus candidates is called.

   6. Remove element from candidates.

   7. Let inclusiveAncestorDocuments be a list consisting of the active document of doc's inclusive ancestor navigables.

   8. If any Document in inclusiveAncestorDocuments has non-null target element, then continue.

   9. Let target be element.

   10. If target is not a focusable area, then set target to the result of getting the focusable area for target.

       Autofocus candidates can contain elements which are not focusable areas. In addition to the special cases handled in the get the focusable area algorithm, this can happen because a non-focusable area element with an autofocus attribute was inserted into a document and it never became focusable, or because the element was focusable but its status changed while it was stored in autofocus candidates.

   11. If target is not null, then:

       1. Empty candidates.

       2. Set topDocument's autofocus processed flag to true.

       3. Run the focusing steps for target.

This handles the automatic focusing during document load. The show() and showModal() methods of dialog elements also processes the autofocus attribute.

Focusing the element does not imply that the user agent has to focus the browser window if it has lost focus.

The autofocus IDL attribute must reflect the content attribute of the same name.

<input maxlength="256" name="q" value="" autofocus>
<input type="submit" value="Search">

<div contenteditable autofocus>Edit <strong>me!</strong><div>

6.7 Assigning keyboard shortcuts

6.7.1 Introduction

This section is non-normative.

Each element that can be activated or focused can be assigned a single key combination to activate it, using the accesskey attribute.

The exact shortcut is determined by the user agent, based on information about the user's keyboard, what keyboard shortcuts already exist on the platform, and what other shortcuts have been specified on the page, using the information provided in the accesskey attribute as a guide.

In order to ensure that a relevant keyboard shortcut is available on a wide variety of input devices, the author can provide a number of alternatives in the accesskey attribute.

Each alternative consists of a single character, such as a letter or digit.

User agents can provide users with a list of the keyboard shortcuts, but authors are encouraged to do so also. The accessKeyLabel IDL attribute returns a string representing the actual key combination assigned by the user agent.

<input type=button value=Collect onclick="collect()"
       accesskey="C 1" id=c>

function addShortcutKeyLabel(button) {
  if (button.accessKeyLabel != '')
    button.value += ' (' + button.accessKeyLabel + ')';
}
addShortcutKeyLabel(document.getElementById('c'));

6.7.2 The accesskey attribute

All HTML elements may have the accesskey content attribute set. The accesskey attribute's value is used by the user agent as a guide for creating a keyboard shortcut that activates or focuses the element.

If specified, the value must be an ordered set of unique space-separated tokens none of which are identical to another token and each of which must be exactly one code point in length.

<nav>
 <p>
  <a title="Consortium Activities" accesskey="A" href="/Consortium/activities">Activities</a> |
  <a title="Technical Reports and Recommendations" accesskey="T" href="/TR/">Technical Reports</a> |
  <a title="Alphabetical Site Index" accesskey="S" href="/Consortium/siteindex">Site Index</a> |
  <a title="About This Site" accesskey="B" href="/Consortium/">About Consortium</a> |
  <a title="Contact Consortium" accesskey="C" href="/Consortium/contact">Contact</a>
 </p>
</nav>

<form action="/search">
 <label>Search: <input type="search" name="q" accesskey="s 0"></label>
 <input type="submit">
</form>

<input type=submit accesskey="N @ 1" value="Compose">
...
<script>
 function labelButton(button) {
   if (button.accessKeyLabel)
     button.value += ' (' + button.accessKeyLabel + ')';
 }
 var inputs = document.getElementsByTagName('input');
 for (var i = 0; i < inputs.length; i += 1) {
   if (inputs[i].type == "submit")
     labelButton(inputs[i]);
 }
</script>

6.7.3 Processing model

An element's assigned access key is a key combination derived from the element's accesskey content attribute. Initially, an element must not have an assigned access key.

Whenever an element's accesskey attribute is set, changed, or removed, the user agent must update the element's assigned access key by running the following steps:

1. If the element has no accesskey attribute, then skip to the fallback step below.

2. Otherwise, split the attribute's value on ASCII whitespace, and let keys be the resulting tokens.

3. For each value in keys in turn, in the order the tokens appeared in the attribute's value, run the following substeps:

   1. If the value is not a string exactly one code point in length, then skip the remainder of these steps for this value.

   2. If the value does not correspond to a key on the system's keyboard, then skip the remainder of these steps for this value.

   3. If the user agent can find a mix of zero or more modifier keys that, combined with the key that corresponds to the value given in the attribute, can be used as the access key, then the user agent may assign that combination of keys as the element's assigned access key and return.

4. Fallback: Optionally, the user agent may assign a key combination of its choosing as the element's assigned access key and then return.

5. If this step is reached, the element has no assigned access key.

Once a user agent has selected and assigned an access key for an element, the user agent should not change the element's assigned access key unless the accesskey content attribute is changed or the element is moved to another Document.

When the user presses the key combination corresponding to the assigned access key for an element, if the element defines a command, the command's Hidden State facet is false (visible), the command's Disabled State facet is also false (enabled), the element is in a document that has a non-null browsing context, and neither the element nor any of its ancestors has a hidden attribute specified, then the user agent must trigger the Action of the command.

User agents might expose elements that have an accesskey attribute in other ways as well, e.g. in a menu displayed in response to a specific key combination.

The accessKey IDL attribute must reflect the accesskey content attribute.

The accessKeyLabel IDL attribute must return a string that represents the element's assigned access key, if any. If the element does not have one, then the IDL attribute must return the empty string.

6.8 Editing

6.8.1 Making document regions editable: The contenteditable content attribute

interface mixin ElementContentEditable {
  [CEReactions] attribute DOMString contentEditable;
  [CEReactions] attribute DOMString enterKeyHint;
  readonly attribute boolean isContentEditable;
  [CEReactions] attribute DOMString inputMode;
};

The contenteditable content attribute is an enumerated attribute with the following keywords and states:

The attribute's missing value default and invalid value default are both the inherit state. The inherit state indicates that the element is editable (or not) based on the parent element's state.

<form method=POST>
 <fieldset>
  <legend>New article</legend>
  <textarea name=article>&lt;p>Hello world.&lt;/p></textarea>
 </fieldset>
 <p><button>Publish</button></p>
</form>

<form method=POST>
 <fieldset>
  <legend>New article</legend>
  <textarea id=textarea name=article>&lt;p>Hello world.&lt;/p></textarea>
  <div id=div style="white-space: pre-wrap" hidden><p>Hello world.</p></div>
  <script>
   let textarea = document.getElementById("textarea");
   let div = document.getElementById("div");
   textarea.hidden = true;
   div.hidden = false;
   div.contentEditable = "true";
   div.oninput = (e) => {
     textarea.value = div.innerHTML;
   };
  </script>
 </fieldset>
 <p><button>Publish</button></p>
</form>

<!doctype html>
<html lang=en>
<title>Live CSS editing!</title>
<style style=white-space:pre contenteditable>
html { margin:.2em; font-size:2em; color:lime; background:purple }
head, title, style { display:block }
body { display:none }
</style>

element.contentEditable [ = value ]

Returns "true", "plaintext-only", "false", or "inherit", based on the state of the contenteditable attribute.

Can be set, to change that state.

Throws a "SyntaxError" DOMException if the new value isn't one of those strings.

element.isContentEditable

✔MDN

HTMLElement/isContentEditable

Support in all current engines.

Firefox4+Safari3+Chrome1+

---

Opera12.1+Edge79+

---

Edge (Legacy)12+Internet Explorer5.5+

---

Firefox Android?Safari iOS1+Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+

Returns true if the element is editable; otherwise, returns false.

The contentEditable IDL attribute, on getting, must return the string "true" if the content attribute is set to the true state, "plaintext-only" if the content attribute is set to the plaintex-only state, "false" if the content attribute is set to the false state, and "inherit" otherwise. On setting, if the new value is an ASCII case-insensitive match for the string "inherit" then the content attribute must be removed, if the new value is an ASCII case-insensitive match for the string "true" then the content attribute must be set to the string "true", if the new value is an ASCII case-insensitive match for the string "plaintext-only" then the content attribute must be set to the string "plaintext-only", if the new value is an ASCII case-insensitive match for the string "false" then the content attribute must be set to the string "false", and otherwise the attribute setter must throw a "SyntaxError" DOMException.

The isContentEditable IDL attribute, on getting, must return true if the element is either an editing host or editable, and false otherwise.

6.8.2 Making entire documents editable: the designMode getter and setter

document.designMode [ = value ]

✔MDN

Document/designMode

Support in all current engines.

Firefox1+Safari1.2+Chrome1+

---

Opera9+Edge79+

---

Edge (Legacy)12+Internet Explorer4+

---

Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android10.1+

Returns "on" if the document is editable, and "off" if it isn't.

Can be set, to change the document's current state. This focuses the document and resets the selection in that document.

Document objects have an associated design mode enabled, which is a boolean. It is initially false.

The designMode getter steps are to return "on" if this's design mode enabled is true; otherwise "off".

The designMode setter steps are:

1. Let value be the given value, converted to ASCII lowercase.

2. If value is "on" and this's design mode enabled is false, then:

   1. Set this's design mode enabled to true.

   2. Reset this's active range's start and end boundary points to be at the start of this.

   3. Run the focusing steps for this's document element, if non-null.

3. If value is "off", then set this's design mode enabled to false.

6.8.3 Best practices for in-page editors

Authors are encouraged to set the 'white-space' property on editing hosts and on markup that was originally created through these editing mechanisms to the value 'pre-wrap'. Default HTML whitespace handling is not well suited to WYSIWYG editing, and line wrapping will not work correctly in some corner cases if 'white-space' is left at its default value.

6.8.4 Editing APIs

An editing host is either an HTML element with its contenteditable attribute in the true state or plaintext-only state, or a child HTML element of a Document whose design mode enabled is true.

The definition of the terms active range, editing host of, and editable, the user interface requirements of elements that are editing hosts or editable, the execCommand(), queryCommandEnabled(), queryCommandIndeterm(), queryCommandState(), queryCommandSupported(), and queryCommandValue() methods, text selections, and the delete the selection algorithm are defined in execCommand. [EXECCOMMAND]

6.8.5 Spelling and grammar checking

User agents can support the checking of spelling and grammar of editable text, either in form controls (such as the value of textarea elements), or in elements in an editing host (e.g. using contenteditable).

For each element, user agents must establish a default behavior, either through defaults or through preferences expressed by the user. There are three possible default behaviors for each element:

true-by-default

The element will be checked for spelling and grammar if its contents are editable and spellchecking is not explicitly disabled through the spellcheck attribute.

false-by-default

The element will never be checked for spelling and grammar unless spellchecking is explicitly enabled through the spellcheck attribute.

inherit-by-default

The element's default behavior is the same as its parent element's. Elements that have no parent element cannot have this as their default behavior.

The spellcheck attribute is an enumerated attribute with the following keywords and states:

The attribute's missing value default and invalid value default are both the default state. The default state indicates that the element is to act according to a default behavior, possibly based on the parent element's own spellcheck state, as defined below.

element.spellcheck [ = value ]

Returns true if the element is to have its spelling and grammar checked; otherwise, returns false.

Can be set, to override the default and set the spellcheck content attribute.

The spellcheck IDL attribute, on getting, must return true if the element's spellcheck content attribute is in the true state, or if the element's spellcheck content attribute is in the default state and the element's default behavior is true-by-default, or if the element's spellcheck content attribute is in the default state and the element's default behavior is inherit-by-default and the element's parent element's spellcheck IDL attribute would return true; otherwise, if none of those conditions applies, then the attribute must instead return false.

The spellcheck IDL attribute is not affected by user preferences that override the spellcheck content attribute, and therefore might not reflect the actual spellchecking state.

On setting, if the new value is true, then the element's spellcheck content attribute must be set to the literal string "true", otherwise it must be set to the literal string "false".

User agents must only consider the following pieces of text as checkable for the purposes of this feature:

• The value of input elements whose type attributes are in the Text, Search, URL, or Email states and that are mutable (i.e. that do not have the readonly attribute specified and that are not disabled).
• The value of textarea elements that do not have a readonly attribute and that are not disabled.
• Text in Text nodes that are children of editing hosts or editable elements.
• Text in attributes of editable elements.

For text that is part of a Text node, the element with which the text is associated is the element that is the immediate parent of the first character of the word, sentence, or other piece of text. For text in attributes, it is the attribute's element. For the values of input and textarea elements, it is the element itself.

To determine if a word, sentence, or other piece of text in an applicable element (as defined above) is to have spelling- and grammar-checking enabled, the UA must use the following algorithm:

1. If the user has disabled the checking for this text, then the checking is disabled.
2. Otherwise, if the user has forced the checking for this text to always be enabled, then the checking is enabled.
3. Otherwise, if the element with which the text is associated has a spellcheck content attribute, then: if that attribute is in the true state, then checking is enabled; otherwise, if that attribute is in the false state, then checking is disabled.
4. Otherwise, if there is an ancestor element with a spellcheck content attribute that is not in the default state, then: if the nearest such ancestor's spellcheck content attribute is in the true state, then checking is enabled; otherwise, checking is disabled.
5. Otherwise, if the element's default behavior is true-by-default, then checking is enabled.
6. Otherwise, if the element's default behavior is false-by-default, then checking is disabled.
7. Otherwise, if the element's parent element has its checking enabled, then checking is enabled.
8. Otherwise, checking is disabled.

If the checking is enabled for a word/sentence/text, the user agent should indicate spelling and grammar errors in that text. User agents should take into account the other semantics given in the document when suggesting spelling and grammar corrections. User agents may use the language of the element to determine what spelling and grammar rules to use, or may use the user's preferred language settings. UAs should use input element attributes such as pattern to ensure that the resulting value is valid, where possible.

If checking is disabled, the user agent should not indicate spelling or grammar errors for that text.

<div contenteditable="true">
 <span spellcheck="false" id="a">Hell</span><em>o!</em>
</div>

<p spellcheck="true">
 <label>Name: <input spellcheck=" false" id="b"></label>
</p>

This specification does not define the user interface for spelling and grammar checkers. A user agent could offer on-demand checking, could perform continuous checking while the checking is enabled, or could use other interfaces.

6.8.6 Autocapitalization

Some methods of entering text, for example virtual keyboards on mobile devices, and also voice input, often assist users by automatically capitalizing the first letter of sentences (when composing text in a language with this convention). A virtual keyboard that implements autocapitalization might automatically switch to showing uppercase letters (but allow the user to toggle it back to lowercase) when a letter that should be autocapitalized is about to be typed. Other types of input, for example voice input, may perform autocapitalization in a way that does not give users an option to intervene first. The autocapitalize attribute allows authors to control such behavior.

The autocapitalize attribute, as typically implemented, does not affect behavior when typing on a physical keyboard. (For this reason, as well as the ability for users to override the autocapitalization behavior in some cases or edit the text after initial input, the attribute must not be relied on for any sort of input validation.)

The autocapitalize attribute can be used on an editing host to control autocapitalization behavior for the hosted editable region, on an input or textarea element to control the behavior for inputting text into that element, or on a form element to control the default behavior for all autocapitalize-inheriting elements associated with the form element.

The autocapitalize attribute never causes autocapitalization to be enabled for input elements whose type attribute is in one of the URL, Email, or Password states. (This behavior is included in the used autocapitalization hint algorithm below.)

The autocapitalization processing model is based on selecting among five autocapitalization hints, defined as follows:

default

The user agent and input method should use make their own determination of whether or not to enable autocapitalization.

none

No autocapitalization should be applied (all letters should default to lowercase).

sentences

The first letter of each sentence should default to a capital letter; all other letters should default to lowercase.

words

The first letter of each word should default to a capital letter; all other letters should default to lowercase.

characters

All letters should default to uppercase.

The autocapitalize attribute is an enumerated attribute whose states are the possible autocapitalization hints. The autocapitalization hint specified by the attribute's state combines with other considerations to form the used autocapitalization hint, which informs the behavior of the user agent. The keywords for this attribute and their state mappings are as follows:

The attribute's missing value default is the default state, and its invalid value default is the sentences state.

element.autocapitalize [ = value ]

Returns the current autocapitalization state for the element, or an empty string if it hasn't been set. Note that for input and textarea elements that inherit their state from a form element, this will return the autocapitalization state of the form element, but for an element in an editable region, this will not return the autocapitalization state of the editing host (unless this element is, in fact, the editing host).

Can be set, to set the autocapitalize content attribute (and thereby change the autocapitalization behavior for the element).

To compute the own autocapitalization hint of an element element, run the following steps:

1. If the autocapitalize content attribute is present on element, and its value is not the empty string, return the state of the attribute.

2. If element is an autocapitalize-inheriting element and has a non-null form owner, return the own autocapitalization hint of element's form owner.

3. Return default.

The autocapitalize getter steps are to:

1. Let state be the own autocapitalization hint of this.

2. If state is default, then return the empty string.

3. If state is none, then return "none".

4. If state is sentences, then return "sentences".

5. Return the keyword value corresponding to state.

The autocapitalize setter steps are to set the autocapitalize content attribute to the given value.

User agents that support customizable autocapitalization behavior for a text input method and wish to allow web developers to control this functionality should, during text input into an element, compute the used autocapitalization hint for the element. This will be an autocapitalization hint that describes the recommended autocapitalization behavior for text input into the element.

User agents or input methods may choose to ignore or override the used autocapitalization hint in certain circumstances.

The used autocapitalization hint for an element element is computed using the following algorithm:

1. If element is an input element whose type attribute is in one of the URL, Email, or Password states, then return default.

2. If element is an input element or a textarea element, then return element's own autocapitalization hint.

3. If element is an editing host or an editable element, then return the own autocapitalization hint of the editing host of element.

4. Assert: this step is never reached, since text input only occurs in elements that meet one of the above criteria.

6.8.7 Input modalities: the inputmode attribute

User agents can support the inputmode attribute on form controls (such as the value of textarea elements), or in elements in an editing host (e.g., using contenteditable).

The inputmode content attribute is an enumerated attribute that specifies what kind of input mechanism would be most helpful for users entering content.

The inputMode IDL attribute must reflect the inputmode content attribute, limited to only known values.

When inputmode is unspecified (or is in a state not supported by the user agent), the user agent should determine the default virtual keyboard to be shown. Contextual information such as the input type or pattern attributes should be used to determine which type of virtual keyboard should be presented to the user.

6.8.8 Input modalities: the enterkeyhint attribute

User agents can support the enterkeyhint attribute on form controls (such as the value of textarea elements), or in elements in an editing host (e.g., using contenteditable).

The enterkeyhint content attribute is an enumerated attribute that specifies what action label (or icon) to present for the enter key on virtual keyboards. This allows authors to customize the presentation of the enter key in order to make it more helpful for users.

The enterKeyHint IDL attribute must reflect the enterkeyhint content attribute, limited to only known values.

When enterkeyhint is unspecified (or is in a state not supported by the user agent), the user agent should determine the default action label (or icon) to present. Contextual information such as the inputmode, type, or pattern attributes should be used to determine which action label (or icon) to present on the virtual keyboard.

6.9 Find-in-page

6.9.1 Introduction

This section defines find-in-page — a common user-agent mechanism which allows users to search through the contents of the page for particular information.

Access to the find-in-page feature is provided via a find-in-page interface. This is a user-agent provided user interface, which allows the user to specify input and the parameters of the search. This interface can appear as a result of a shortcut or a menu selection.

A combination of text input and settings in the find-in-page interface represents the user query. This typically includes the text that the user wants to search for, as well as optional settings (e.g., the ability to restrict the search to whole words only).

The user-agent processes page contents for a given query, and identifies zero or more matches, which are content ranges that satisfy the user query.

One of the matches is identified to the user as the active match. It is highlighted and scrolled into view. The user can navigate through the matches by advancing the active match using the find-in-page interface.

Issue #3539 tracks standardizing how find-in-page underlies the currently-unspecified window.find() API.

6.9.2 Interaction with details and hidden=until-found

When find-in-page begins searching for matches, all details elements in the page which do not have their open attribute set should have the skipped contents of their second slot become accessible, without modifying the open attribute, in order to make find-in-page able to search through it. Similarly, all HTML elements with the hidden attribute in the hidden until found state should have their skipped contents become accessible without modifying the hidden attribute in order to make find-in-page able to search through them. After find-in-page finishes searching for matches, the details elements and the elements with the hidden attribute in the hidden until found state should have their contents become skipped again. This entire process must happen synchronously (and so is not observable to users or to author code). [CSSCONTAIN]

When find-in-page chooses a new active match, perform the following steps:

1. Let node be the first node in the active match.

2. Queue a global task on the user interaction task source given node's relevant global object to run the following steps:

   1. Run the ancestor details revealing algorithm on node.

   2. Run the ancestor hidden-until-found revealing algorithm on node.

When find-in-page auto-expands a details element like this, it will fire a toggle event. As with the separate scroll event that find-in-page fires, this event could be used by the page to discover what the user is typing into the find-in-page dialog. If the page creates a tiny scrollable area with the current search term and every possible next character the user could type separated by a gap, and observes which one the browser scrolls to, it can add that character to the search term and update the scrollable area to incrementally build the search term. By wrapping each possible next match in a closed details element, the page could listen to toggle events instead of scroll events. This attack could be addressed for both events by not acting on every character the user types into the find-in-page dialog.

6.9.3 Interaction with selection

The find-in-page process is invoked in the context of a document, and may have an effect on the selection of that document. Specifically, the range that defines the active match can dictate the current selection. These selection updates, however, can happen at different times during the find-in-page process (e.g. upon the find-in-page interface dismissal or upon a change in the active match range).

6.10 Close requests and close watchers

6.10.1 Close requests

In an implementation-defined (and likely device-specific) manner, a user can send a close request to the user agent. This indicates that the user wishes to close something that is currently being shown on the screen, such as a popover, menu, dialog, picker, or display mode.

Whenever the user agent receives a potential close request targeted at a Document document, it must queue a global task on the user interaction task source given document's relevant global object to perform the following close request steps:

1. If document's fullscreen element is not null, then:

   1. Fully exit fullscreen given document's node navigable's top-level traversable's active document.

   2. Return.

   This does not fire any relevant event, such as keydown; it only causes fullscreenchange to be eventually fired.

2. Fire any relevant events, per UI Events or other relevant specifications. [UIEVENTS]

   An example of relevant events in the UI Events model would be the keydown and keyup sequence that UI Events suggests firing when the user presses the Esc key on their keyboard. On most platforms with keyboards, this is treated as a close request, and so would trigger these close request steps.

   An example of relevant events that are outside of the model given in UI Events would be assistive technology synthesizing an Esc keydown and keyup sequence when the user sends a close request by using a dismiss gesture.

3. Let event be null if no such events are fired, or the Event object representing one of the fired events otherwise. If multiple events are fired, which one is chosen is implementation-defined, except that if keydown and keyup events were fired for the Esc key, the user agent must pick the keyup event.

4. If event is not null, and its canceled flag is set, then return.

5. If document is not fully active, then return.

   This step is necessary because, if event is not null, then an event listener might have caused document to no longer be fully active.

6. Let closedSomething be the result of processing close watchers on document's relevant global object.

7. If closedSomething is true, then return.

8. Otherwise, there was nothing watching for a close request. The user agent may instead interpret this interaction as some other action, instead of interpreting it as a close request.

On platforms where Esc is the close request, the user agent will first fire an appropriately-initialized keydown and keyup event sequence. If the web developer cancels the keyup event by calling preventDefault(), then nothing further happens. But if the event fires without being canceled, then the user agent proceeds to process close watchers.

On platforms where a back button is a potential close request, no event is involved, so when the back button is pressed, the user agent proceeds directly to process close watchers. If there is a close watcher on the close watcher stack, then that will get triggered. If there is not, then the user agent can interpret the back button press in another way, for example as a request to traverse the history by a delta of −1.

6.10.2 Close watcher infrastructure

Each Window has a close watcher stack, a list of close watchers, initially empty.

It isn't quite a proper stack, as items can get removed from the middle of it if a close watcher is destroyed or closed via web developer code. User-initiated close requests always act on the top of the close watcher stack, however.

A close watcher is a struct with the following items:

• A window, a Window.

• A cancel action, a list of steps. These steps can never throw an exception, and return either true (to indicate that the caller will proceed to the close action) or false (to indicate that the caller will bail out).

• A close action, a list of steps. These steps can never throw an exception.

• A was created with user activation boolean.

• An is grouped with previous boolean.

• An is running cancel action boolean.

The is grouped with previous boolean is set if a close watcher is created without history-action activation. (Except the very first close watcher in the close watcher stack that is created without transient activation, which gets a pass on this restriction.) It causes a user-triggered close request to close all such grouped-together close watchers, thus ensuring that web developers can't make close requests ineffective by creating an excessive number of close watchers.

A close watcher closeWatcher is active if closeWatcher's window's close watcher stack contains closeWatcher.

To establish a close watcher given a Window window, a list of steps cancelAction, and a list of steps closeAction:

1. Assert: window's associated Document is fully active.

2. Let wasCreatedWithUserActivation and isGroupedWithPrevious be null.

3. If window has history-action activation, then:

   1. Consume history-action user activation given window.

   2. Set wasCreatedWithUserActivation to true.

   3. Set isGroupedWithPrevious to false.

4. Otherwise, if there is no close watcher in window's close watcher stack whose was created with user activation is false, then:

   1. Set wasCreatedWithUserActivation to false.

   2. Set isGroupedWithPrevious to false.

   This will be the one "free" close watcher created without user activation, which is useful for cases like session inactivity timeout dialogs or notifications from the server.

5. Otherwise:

   1. Set wasCreatedWithUserActivation to false.

   2. Set isGroupedWithPrevious to true.

6. Let closeWatcher be a new close watcher, with

   window

   window

   cancel action

   cancelAction

   close action

   closeAction

   was created with user activation

   wasCreatedWithUserActivation

   is grouped with previous

   isGroupedWithPrevious

   is running cancel action

   false

7. Append closeWatcher to window's close watcher stack.

8. Return closeWatcher.

To request to close a close watcher closeWatcher:

1. If closeWatcher is not active, then return.

2. If closeWatcher's is running cancel action is true, then return.

3. Let window be closeWatcher's window.

4. If window's associated Document is not fully active, then return.

5. If window has history-action activation, then:

   1. Set closeWatcher's is running cancel action to true.

   2. Let shouldContinue be the result of running closeWatcher's cancel action.

   3. Set closeWatcher's is running cancel action to false.

   4. If shouldContinue is false, then:

      1. Consume history-action user activation given window.

      2. Return.

   The guard on these substeps means that the cancel action only has a chance to prevent us from continuing onward to the close action when window has history-action activation. In particular, since these substeps consume history-action user activation, requesting to close a close watcher twice without any intervening user activation will skip these substeps.

6. Close closeWatcher.

To close a close watcher closeWatcher:

1. If closeWatcher is not active, then return.

2. If closeWatcher's window's associated Document is not fully active, then return.

3. Destroy closeWatcher.

4. Run closeWatcher's close action.

To destroy a close watcher closeWatcher, remove closeWatcher from closeWatcher's window's close watcher stack.

To process close watchers given a Window window:

1. Let processedACloseWatcher be false.

2. While window's close watcher stack is not empty:

   1. Let closeWatcher be the last item in window's close watcher stack.

   2. Request to close closeWatcher.

   3. Set processedACloseWatcher to true.

   4. If closeWatcher's is grouped with previous is false, then break.

3. Return processedACloseWatcher.

6.10.3 The CloseWatcher interface

[Exposed=Window]
interface CloseWatcher : EventTarget {
  constructor(optional CloseWatcherOptions options = {});

  undefined requestClose();
  undefined close();
  undefined destroy();

  attribute EventHandler oncancel;
  attribute EventHandler onclose;
};

dictionary CloseWatcherOptions {
  AbortSignal signal;
};

watcher = new CloseWatcher()

watcher = new CloseWatcher({ signal })

Creates a new CloseWatcher instance.

If the signal option is provided, then watcher can be destroyed (as if by watcher.destroy()) by aborting the given AbortSignal.

If any close watcher is already active, and the Window does not have history-action activation, then the resulting CloseWatcher will be closed together with that already-active close watcher in response to any close request. (This already-active close watcher does not necessarily have to be a CloseWatcher object; it could be a modal dialog element, or a popover generated by an element with the popover attribute.)

watcher.requestClose()

Acts as if a close request was sent targeting watcher, by first firing a cancel event, and if that event is not canceled with preventDefault(), proceeding to fire a close event before deactivating the close watcher as if watcher.destroy() was called.

This is a helper utility that can be used to consolidate cancelation and closing logic into the cancel and close event handlers, by having all non-close request closing affordances call this method.

watcher.close()

Immediately fires the close event, and then deactivates the close watcher as if watcher.destroy() was called.

This is a helper utility that can be used trigger the closing logic into the close event handler, skipping any logic in the cancel event handler.

watcher.destroy()

Deactivates watcher, so that it will no longer receive close events and so that new independent CloseWatcher instances can be constructed.

This is intended to be called if the relevant UI element is torn down in some other way than being closed.

Each CloseWatcher instance has an internal close watcher, which is a close watcher.

The new CloseWatcher(options) constructor steps are:

1. If this's relevant global object's associated Document is not fully active, then throw an "InvalidStateError" DOMException.

2. Let closeWatcher be the result of establishing a close watcher given this's relevant global object, with:

   • cancelAction being to return the result of firing an event named cancel at this, with the cancelable attribute initialized to true.

   • closeAction being to fire an event named close at this.

3. If options["signal"] exists, then:

   1. If options["signal"] is aborted, then destroy closeWatcher.

   2. Add the following steps to options["signal"]:

      1. Destroy closeWatcher.

4. Set this's internal close watcher to closeWatcher.

The requestClose() method steps are to request to close this's internal close watcher.

The close() method steps are to close this's internal close watcher.

The destroy() method steps are to destroy this's internal close watcher.

The following are the event handlers (and their corresponding event handler event types) that must be supported, as event handler IDL attributes, by all objects implementing the CloseWatcher interface:

const watcher = new CloseWatcher();
const picker = setUpAndShowPickerDOMElement();

let chosenValue = null;

watcher.onclose = () => {
  chosenValue = picker.querySelector('input').value;
  picker.remove();
};

picker.querySelector('.close-button').onclick = () => watcher.requestClose();