6 User interaction

6.1 The hidden attribute

All HTML elements may have the hidden content attribute set. The hidden attribute is a boolean attribute. When specified on an element, 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.

Because this attribute is typically implemented using CSS, it's also possible to override it using CSS. For instance, a rule that applies 'display: block' to all elements will cancel the effects of the hidden attribute. Authors therefore have to take care when writing their style sheets to make sure that the attribute is still styled as expected.

In the following skeletal example, the attribute is used to hide the Web game's main screen until the user logs in:

  <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.

For example, it would be incorrect to use the href attribute to link to a section marked with the hidden attribute. If the content is not applicable or relevant, then there is no reason to link to it.

It would be fine, however, to use the ARIA aria-describedby attribute to refer to descriptions that are themselves hidden. While hiding the descriptions implies that they are not useful alone, they could be written in such a way that they are useful in the specific context of being referenced from the images that they describe.

Similarly, a canvas element with the hidden attribute could be used by a scripted graphics engine as an off-screen buffer, and a form control could refer to a hidden form element using its form attribute.

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.

6.2 Inert subtrees

A node (in particular elements and text nodes) can be marked as inert. When a node is inert, then the user agent must act as if the node was absent for the purposes of targeting user interaction events, may ignore the node for the purposes of text search user interfaces (commonly known as "find in page"), and may prevent the user from selecting text in that node. User agents should allow the user to override the restrictions on search and text selection, however.

For example, consider a page that consists of just a single inert paragraph positioned in the middle of a body. If a user moves their pointing device from the body over to the inert paragraph and clicks on the paragraph, no mouseover event would be fired, and the mousemove and click events would be fired on the body element rather than the paragraph.

When a node is inert, it generally cannot be focused. Inert nodes that are commands will also get disabled.

While a browsing context container is marked as inert, its nested browsing context's active document, and all nodes in that Document, must be marked as inert.

An entire Document can be marked as blocked by a modal dialog subject. While a Document is so marked, every node that is in the Document, with the exception of the subject element and its descendants, must be marked inert. (The elements excepted by this paragraph can additionally be marked inert through other means; being part of a modal dialog does not "protect" a node from being marked inert.)

Only one element at a time can mark a Document as being blocked by a modal dialog. When a new dialog is made to block a Document, the previous element, if any, stops blocking the Document.

The dialog element's showModal() method makes use of this mechanism.

6.3 Activation

Certain elements in HTML have an activation behavior, which means that the user can activate them. This triggers a sequence of events dependent on the activation mechanism, and normally culminating in a click event.

element . click()

Acts as if the element was clicked.

6.4 Focus

6.4.1 Introduction

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.

Consider an HTML application running in a browser tab running in a graphical environment. Suppose this application had a page with some text fields and links, and was currently showing a modal dialog, which itself had a text field and a button.

The hierarchy of focusable widgets, in this scenario, would include the browser window, which would have, amongst its children, the browser tab containing the HTML application. The tab itself would have as its children the various links and text fields, as well as the dialog. The dialog itself would have as its children the text field and the button.

If the widget with focus in this example was the text field in the dialog box, then key input would be channeled from the graphical system to ① the Web browser, then to ② the tab, then to ③ the dialog, and finally to ④ the text field.

Keyboard events are always targetted at this focused element.

6.4.2 Data model

The term focusable area is used to refer to regions of the interface that can become the target of 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.)

Focusable area DOM anchor
Examples
Elements that have their tabindex focus flag set, that are not actually disabled, that are not expressly inert, and that are either being rendered or being used as relevant canvas fallback content. The element itself.

iframe, <input type=text>, sometimes <a href=""> (depending on platform conventions).

The shapes of area elements in an image map associated with an img element that is being rendered and is not expressly inert. The img element.

In the following example, the area element creates two shapes, one on each image. The DOM anchor of the first shape is the first img element, and the DOM anchor of the second shape is the second img element.

<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">
The user-agent provided subwidgets of elements that are being rendered and are not actually disabled or expressly inert. The element for which the focusable area is a subwidget.

The controls in the user interface that is exposed to the user for a video element, the up and down buttons in a spin-control version of <input type=number>, the two range control widgets in a <input type=range multiple>, the part of a details element's rendering that enabled the element to be opened or closed using keyboard input.

The scrollable regions of elements that are being rendered are not expressly inert. The element for which the box that the scrollable region scrolls was created.

The CSS 'overflow' property's 'scroll' value typically creates a scrollable region.

The viewport of a Document that is in a browsing context and is not inert. The Document for which the viewport was created.

The contents of an iframe.

Any other element or part of an element, especially to aid with accessibility or to better match platform conventions. The element.

A user agent could make all list item bullets focusable, so that a user can more easily navigate lists.

Similarly, a user agent could make all elements with title attributes focusable, so that their advisory information can be accessed.

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

Each focusable area belongs to a control group. Each control group has an owner. Control group owners are control group owner objects. The following are control group owner objects:

Each control group owner object owns one control group (though that group might be empty).

If the DOM anchor of a focusable area is a control group owner object, then that focusable area belongs to that control group owner object's control group. Otherwise, the focusable area belongs to its DOM anchor's nearest ancestor control group owner object.

Thus, a viewport always belongs to the control group of the Document for which the viewport was created, an input control belongs to the control group of its nearest ancestor dialog or Document, and an image map's shapes belong to the nearest ancestor dialog or Document of the img elements (not the area elements — this means one area element might create multiple shapes in different control groups).

An element is expressly inert if it is inert but it is not a control group owner object and its nearest ancestor control group owner object is not inert.

One focusable area in each non-empty control group is designated the focused area of the control group. Which control is so designated changes over time, based on algorithms in this specification. If a control group is empty, it has no focused area.

Each control group owner object can also act as the manager of a dialog group.

Each dialog element that has an open attribute specified and that is being rendered (i.e. that is a control group owner object) and is not expressly inert belongs to the dialog group whose manager is the dialog element's nearest ancestor control group owner object.

A dialog is expressly inert if it is inert but its nearest ancestor control group owner object is not.

If no dialog element has a particular control group owner object as its nearest ancestor control group owner object, then that control group owner object has no dialog group.

Each dialog group can have a dialog designated as the focused dialog of the dialog group. Which dialog is so designated changes over time, based on algorithms in this specification.


Focusable areas in control groups are ordered relative to the tree order of their DOM anchors. Focusable areas with the same DOM anchor in a control group are ordered relative to their CSS box's relative positions in a pre-order, depth-first traversal of the box tree. [CSS]

Elements in dialog groups are ordered in tree order.


The currently focused area of a top-level browsing context at any particular time is the focusable area or dialog returned by this algorithm:

  1. Let candidate be the Document of the top-level browsing context.

  2. If candidate has a dialog group with a designated focused dialog of the dialog group, then let candidate be the designated focused dialog of the dialog group, and redo this step.

    Otherwise, if candidate has a non-empty control group, and the designated focused area of the control group is a browsing context container, then let candidate be the active document of that browsing context container's nested browsing context, and redo this step.

    Otherwise, if candidate has a non-empty control group, let candidate be the designated focused area of the control group.

  3. Return candidate.

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 browsing context. When an element is the DOM anchor of a focusable area of the currently focused area of a top-level browsing context, it is focused.

6.4.3 The tabindex attribute

The tabindex content attribute allows authors to indicate that an element is supposed to be focusable, and whether it is supposed to be reachable using sequential focus navigation and, if so, what is to be the relative order of the element for the purposes of 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 the focusable elements that can be reached using sequential focus navigation.

When the attribute is omitted, the user agent applies defaults. (There is no way to make an element that is being rendered be not focusable at all without disabling it or making it inert.)

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 to be unreachable by sequential focus navigation.

6.4.4 Focus management APIs

document . activeElement

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 browsing context is focused, its browsing context container is focused in the parent browsing context. For example, if the user moves the focus to a text field in an iframe, the iframe is the element returned by the activeElement API in the iframe's Document.

document . hasFocus()

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 documented nested inside this one, being focused.

window . focus()

Moves the focus to the window's browsing context container, if any.

element . focus()

Moves the focus to the element.

If the element is the body element, moves the focus to the viewport instead.

element . blur()

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 body element.

Do not use this method to hide the focus ring if you find the focus ring unsightly. Instead, use a CSS rule 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 links and instead use a yellow background to indicate focus, you could use:

:link:focus, :visited:focus { outline: none; background: yellow; color: black; }

6.5 Assigning keyboard shortcuts

6.5.1 Introduction

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.

In this example, an author has provided a button that can be invoked using a shortcut key. To support full keyboards, the author has provided "C" as a possible key. To support devices equipped only with numeric keypads, the author has provided "1" as another possibly key.

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

To tell the user what the shortcut key is, the author has this script here opted to explicitly add the key combination to the button's label:

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

Browsers on different platforms will show different labels, even for the same key combination, based on the convention prevalent on that platform. For example, if the key combination is the Control key, the Shift key, and the letter C, a Windows browser might display "Ctrl+Shift+C", whereas a Mac browser might display "^⇧C", while an Emacs browser might just display "C-C". Similarly, if the key combination is the Alt key and the Escape key, Windows might use "Alt+Esc", Mac might use "⌥⎋", and an Emacs browser might use "M-ESC" or "ESC ESC".

In general, therefore, it is unwise to attempt to parse the value returned from the accessKeyLabel IDL attribute.

6.5.2 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 that are case-sensitive, each of which must be exactly one Unicode code point in length.

In the following example, a variety of links are given with access keys so that keyboard users familiar with the site can more quickly navigate to the relevant pages:

<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>

In the following example, the search field is given two possible access keys, "s" and "0" (in that order). A user agent on a device with a full keyboard might pick Ctrl+Alt+S as the shortcut key, while a user agent on a small device with just a numeric keypad might pick just the plain unadorned key 0:

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

In the following example, a button has possible access keys described. A script then tries to update the button's label to advertise the key combination the user agent selected.

<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>

On one user agent, the button's label might become "Compose (⌘N)". On another, it might become "Compose (Alt+⇧+1)". If the user agent doesn't assign a key, it will be just "Compose". The exact string depends on what the assigned access key is, and on how the user agent represents that key combination.

6.6 Editing

6.6.1 Making document regions editable: The contenteditable content attribute

The contenteditable attribute is an enumerated attribute whose keywords are the empty string, true, and false. The empty string and the true keyword map to the true state. The false keyword maps to the false state. In addition, there is a third state, the inherit state, which is the missing value default (and the invalid value default).

The true state indicates that the element is editable. The inherit state indicates that the element is editable if its parent is. The false state indicates that the element is not editable.

element . contentEditable [ = value ]

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

Can be set, to change that state.

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

element . isContentEditable

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

6.6.2 Making entire documents editable: The designMode IDL attribute

document . designMode [ = value ]

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.

6.6.3 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.

As an example of problems that occur if the default 'normal' value is used instead, consider the case of the user typing "yellow&blank;&blank;ball", with two spaces (here represented by "&blank;") between the words. With the editing rules in place for the default value of 'white-space' ('normal'), the resulting markup will either consist of "yellow&nbsp; ball" or "yellow &nbsp;ball"; i.e., there will be a non-breaking space between the two words in addition to the regular space. This is necessary because the 'normal' value for 'white-space' requires adjacent regular spaces to be collapsed together.

In the former case, "yellow⍽" might wrap to the next line ("⍽" being used here to represent a non-breaking space) even though "yellow" alone might fit at the end of the line; in the latter case, "⍽ball", if wrapped to the start of the line, would have visible indentation from the non-breaking space.

When 'white-space' is set to 'pre-wrap', however, the editing rules will instead simply put two regular spaces between the words, and should the two words be split at the end of a line, the spaces would be neatly removed from the rendering.

6.6.4 Editing APIs

The definition of the terms active range, editing host, 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 the HTML Editing APIs specification. The interaction of editing and the undo/redo features in user agents is defined by the UndoManager and DOM Transaction specification. [EDITING] [UNDO]

6.6.5 Spelling and grammar checking

The spellcheck attribute is an enumerated attribute whose keywords are the empty string, true and false. The empty string and the true keyword map to the true state. The false keyword maps to the false state. In addition, there is a third state, the default state, which is the missing value default (and the invalid value default).

The true state indicates that the element is to have its spelling and grammar checked. 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. The false state indicates that the element is not to be checked.

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.

element . forceSpellCheck()

Forces the user agent to report spelling and grammar errors on the element (if checking is enabled), even if the user has never focused the element. (If the method is not invoked, user agents can hide errors in text that wasn't just entered by the user.)

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.