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<!DOCTYPE html>
<html lang='en'>
<head>
<meta charset='utf-8'>
<title>
EditContext API
</title>
<script src='https://www.w3.org/Tools/respec/respec-w3c' defer class=
'remove'></script>
<script class='remove'>
var respecConfig = {
github: "w3c/edit-context"
,specStatus: "ED"
,shortName: "edit-context"
,editors: [{ name: "Shih-ling Keng",
mailto: "[email protected]",
company: "Microsoft",
w3cid: 126951},
{ name: "Anupam Snigdha",
mailto: "[email protected]",
company: "Microsoft",
w3cid: 126950},
{ name: "Bo Cupp",
mailto: "[email protected]",
company: "Microsoft",
w3cid: 126951},
{ name: "Dan Clark",
mailto: "[email protected]",
company: "Microsoft",
w3cid: 113024},]
, wgPublicList: "public-editing-tf"
, otherLinks: [{
key: 'Participate',
data: [{
value: 'We are on GitHub.',
href: 'https://github.com/w3c/edit-context'
}, {
value: 'File a bug.',
href: 'https://github.com/w3c/edit-context/issues'
}, {
value: 'Commit history.',
href: 'https://github.com/w3c/edit-context/commits/gh-pages'
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value: 'Mailing list.',
href: 'http://lists.w3.org/Archives/Public/public-editing-tf/'
}]
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, group: "webediting"
, edDraftURI: "https://w3c.github.io/edit-context/"
, xref: ["WebIDL"
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, "uievents"
, "infra"
, "input-events"]
};
</script>
</head>
<body>
<section id='abstract'>
<p>
{{EditContext}} is an API that allows authors to more directly participate in
the text input process.
</p>
</section>
<section id='sotd'></section>
<section>
<h2>
Introduction
</h2>
<section id="background" class="informative">
<h3>
Background and Motivation
</h3>
<p>
Modern operating systems provide mechanisms to produce text in a variety of
ways: speech-to-text, virtual keyboards, handwriting recognition and many more.
When an app wants to consume text input from these various sources, it must
first provide a view of its currently editable text to the operating system.
The view of editable text provides a common language that apps (having a
variety of different document models) and sources of text (having a variety of
different input methods) can both understand. Both the apps and input sources
communicate with one another by expressing their desired changes to the state
of the common view as an event that the other can handle to facilitate the text
input process.
</p>
<p>
For the purposes of this document, a producer of text is known as a <dfn>Text
Input Method</dfn>. The view provided by an app which wants to consume text is
called a <dfn>Text Edit Context</dfn>. The service provided by the OS to
facilitate the editing of text in the [=Text Edit Context=] by the [=Text Input
Methods=] is called a <dfn>Text Input Service</dfn>.
</p>
<figure id="many-input-methods">
<img src="images/many-input-methods.jpg" alt="">
<figcaption>
Many [=Text Input Methods=] using a [=Text Input Service=] to communicate with
many apps through their [=Text Edit Contexts=].
</figcaption>
</figure>
<p>
Here’s a typical flow for the text input process in more detail:
</p>
<ol>
<li>A user places focus into an editable region of the app.
</li>
<li>The app produces a [=Text Edit Context=] describing its editable region
according to the standards set forth by the [=Text Input Service=] and provides
that [=Text Edit Context=] to the [=Text Input Service=].
</li>
<li>The [=Text Input Service=] triggers a [=Text Input Method=] to provide some
user interface for capturing text input from the user and provides the [=Text
Input Method=] the app generated [=Text Edit Context=].
</li>
<li>The [=Text Input Method=] reads the location of selection and nearby text
from the [=Text Edit Context=] to help tailor its user experience.
</li>
<li>The [=Text Input Method=] may also read screen coordinates for where the
selection and editable region are located so that it can properly position its
user interface next to the text being edited.
</li>
<li>The user interacts with the [=Text Input Method=] user interface to input
text in some [=Text Input Method=]-specific way.
</li>
<li>The [=Text Input Method=] describes its desired modifications to the text
and selection in the [=Text Edit Context=] in response to the user’s input.
</li>
<li>The app handles an event describing the desired modifications to its [=Text
Edit Context=] and renders the result to the user.
</li>
</ol>
<figure id="text-input-process">
<img src="images/text-input-process.jpg" alt="">
<figcaption>
A sequence diagram illustrating a typical flow for text input.
</figcaption>
</figure>
<p>
Existing user agents handle the details of this text input process so that the
author’s responsibility ends at declaring what elements of the document
represent an editable region. Authors express which regions are editable using
input elements, textarea elements, contenteditable elements, or by setting the
{{Document/designMode}} attribute to "<code>on</code>" to mark an entire
document as editable.
</p>
<p>
As an editable region of the document is <a href=
"https://html.spec.whatwg.org/multipage/interaction.html#focused">focused</a>,
the user agent automatically produces the [=Text Edit Context=] from the
contents of the editable region and the position of the selection within it.
When a [=Text Input Method=] produces text, the user agent translates the
events against its [=Text Edit Context=] into a set of DOM and style
modifications – only some of which are described using existing events that an
author can handle.
</p>
<p>
Authors that want to produce sophisticated editing experiences may be
challenged by the current approach. If, for example, the text and selection are
rendered to a canvas, user agents are unable to produce a [=Text Edit Context=]
to drive the text input process. Authors compensate by resorting to offscreen
editable elements, but this approach comes with negative implications for
accessibility, it deteriorates the input experience, and requires complex code
to synchronize the position of the text in the offscreen editable element with
the corresponding text in the canvas.
</p>
<p>
With the introduction of this EditContext API, authors can more directly
participate in the protocol for text input and avoid the pitfalls described
above.
</p>
</section>
<section id="editcontext-model">
<h3>
The EditContext Model
</h3>
<p>
The [=Text Input Service=] and [=Text Edit Context=] are abstractions
representing the common aspects of text input across many operating systems. An
{{EditContext}} is a JavaScript reflection of the [=Text Edit Context=]. When
changes are made to the [=Text Edit Context=] by the [=Text Input Service=],
those changes are reflected to the author asynchronously in the form of events
which are dispatched against the [=active EditContext=]. When the author makes
changes to the [=active EditContext=], those changes will be reflected in the
[=Text Edit Context=] during the next lifecycle update.
</p>
<h4>
EditContext state
</h4>
<p>
Both the [=Text Edit Context=] and {{EditContext}} have a [=text state=] which
holds the information exchanged in the aforementioned updates. The <dfn>text
state</dfn> consists of:
</p>
<ul>
<li>
<dfn>text</dfn> which is a {{DOMString}} representing editable content. The
initial value is the empty string.
</li>
<li>
<dfn>selection start</dfn> which refers to the offset in [=text=] where the
selection starts. The initial value is 0.
</li>
<li>
<dfn>selection end</dfn> which refers to the offset in [=text=] where the
selection ends. The initial value is 0. [=selection end=] may be less than
[=selection start=] in the case of a "backwards" selection (in reverse of
document order).
</li>
<li>
<dfn>is composing</dfn> which indicates if there is an active composition. The
initial value is false.
</li>
<li>
<dfn>composition start</dfn> which refers to the offset in [=text=]
representing the start position of the text being actively composed. The
initial value is 0.
</li>
<li>
<dfn>composition end</dfn> which refers to the offset in [=text=] representing
the end position of the text being actively composed. The initial value is 0.
[=composition end=] must always be greater than or equal to [=composition
start=].
</li>
<li>
<dfn>text formats</dfn> which is an array of [=text format=]. The array is
initially empty.
</li>
<li>
<dfn>control bounds</dfn> is a {{DOMRect}} describing the area of the viewport
in which [=text=] is displayed. It is in the [=client coordinate system=] and
the initial x, y, width, and height are all 0.
</li>
<li>
<dfn>selection bounds</dfn> is a {{DOMRect}} describing the position of
selection. It is in the [=client coordinate system=] and the initial x, y,
width, and height are all 0.
</li>
<li>
<dfn>codepoint rects start index</dfn> which is an offset into [=text=] that
respresents the position before the first codepoint whose location is reported
by the first member of [=codepoint rects=] array.
</li>
<li>
<dfn>codepoint rects</dfn> is an array of {{DOMRect}} defining the bounding box
of each codepoint. The array is initially empty.
</li>
</ul>
<p>
<dfn>text format</dfn> is a struct that indicates decorative properties that
should be applied to the ranges of [=text=]. The struct contains:
</p>
<ul>
<li>
<dfn>range start</dfn> which is an offset into [=text=] that respresents the
position before the first codepoint that should be decorated.
</li>
<li>
<dfn>range end</dfn> which is an offset into [=text=] that respresents the
position after the last codepoint that should be decorated.
</li>
<li>
<dfn>underline style</dfn>, a {{UnderlineStyle}} which is the preferred
underline style of the decorated [=text=] range.
</li>
<li>
<dfn>underline thickness</dfn>, a {{UnderlineThickness}} which is the preferred
underline thickness of the decorated [=text=] range.
</li>
</ul>
<p class="note">
[=Codepoint rects=] provides the means for the user agent to query a range of
[=text=] for positioning information. The [=Text Input Service=] will use this
information, in tandem with the [=control bounds=] and [=selection bounds=], to
support the Text Input Method in properly displaying its user interface. For
example, the info can be used to position an IME window adjacent to text being
composed. Different platforms may require different positions to be cached to
fulfill queries from the [=Text Input Service=]. The user agent will indicate
which positions are required by firing {{CharacterBoundsUpdateEvent}}.
</p>
<p>
[=Control bounds=], [=selection bounds=], and [=codepoint rects=] are given in
the <dfn>client coordinate system</dfn>, which is defined as a two-dimensional
Cartesian coordinate system (x, y) where the origin is the top-left corner of
the <a href="https://drafts.csswg.org/cssom-view/#layout-viewport">layout
viewport</a>, the x-axis points towards the top-right of the <a href=
"https://drafts.csswg.org/cssom-view/#layout-viewport">layout viewport</a>, and
the y-axis points towards the bottom-left of the <a href=
"https://drafts.csswg.org/cssom-view/#layout-viewport">layout viewport</a>. The
units of the client coordinate system are <a href=
"https://drafts.csswg.org/css-values/#px">CSS pixels</a>.
</p>
<div class="note">
<p>
Since EditContext bounds are defined in <a data-lt=
"client coordinate system">client coordinates</a>, the coordinates indicating a
given piece of content on a page will change as the user scrolls the document
even if the content itself does not change position in the document. A scenario
where authors may want to take this into account is the case where the user
scrolls the page where the user has an active composition. If the author does
not update the EditContext's bounds information (e.g. during a scroll event
listener), the IME window may no longer line up with the text being composed
for the duration of the composition.
</p>
<p>
However, some platforms do not adjust IME windows during an active composition,
so updating bounds information mid-composition does not guarantee that the IME
window will be repositioned until it's closed and reopened.
</p>
</div>
<h4>
Association and activation
</h4>
<p>
An {{EditContext}} has an <dfn data-for="edit-context">associated
element</dfn>, an {{HTMLElement}}. An element becomes an {{EditContext}}'s
<a>associated element</a> by assigning the {{EditContext}} to the element's
{{HTMLElement/editContext}} property. An {{HTMLElement}} can be <a data-lt=
"associated element">associated</a> with at most one {{EditContext}}.
</p>
<p class="note">
An {{EditContext}} keeps its [=associated element=] alive, so developers should
be aware that assigning an {{EditContext}} to an element's
{{HTMLElement/editContext}} property will prevent the element from being
garbage collected until the property is cleared or the {{EditContext}} is
garbage collected.
</p>
<p>
If an {{EditContext}}'s <a>associated element</a>'s <a href=
"https://dom.spec.whatwg.org/#concept-tree-parent">parent</a> is not <a href=
"https://w3c.github.io/editing/docs/execCommand/#editable">editable</a> and is
not a [=Document=] whose {{Document/designMode}} attribute is
"<code>on</code>", then the <a>associated element</a> becomes an <dfn class=
"export">EditContext editing host</dfn>. An <a>EditContext editing host</a> is
a type of [=editing host=] whose behaviors are described in
[[[#edit-context-differences]]].
</p>
<div class="note">
<p>
There are a couple implications of this. Firstly, if an element that is already
an [=editing host=] due to [^html-global/contenteditable^] becomes an
{{EditContext}}'s <a>associated element</a>, then that element becomes an
<a>EditContext editing host</a>. In other words, if both {{EditContext}} and
[^html-global/contenteditable^] are set on an element, the EditContext behavior
"wins".
</p>
<p>
Secondly, if an element is <a href=
"https://w3c.github.io/editing/docs/execCommand/#editable">editable</a> but not
an [=editing host=] (i.e. it is a child in the subtree of an [=editing host=]),
then becoming an {{EditContext}}'s <a>associated element</a> has no effect on
that element. This is analogous to the behavior of
[^html-global/contenteditable^], where setting [^html-global/contenteditable^]
to "<code>true</code>" on an <a href=
"https://w3c.github.io/editing/docs/execCommand/#editable">editable</a> element
that is not an [=editing host=] has no effect. Taken together, these rules
imply that an editable tree of nodes will follow either the {{EditContext}}
behavior or non-{{EditContext}} behavior, but the behaviors cannot be mixed.
</p>
</div>
<p>
A {{Document}} has an <dfn>active EditContext</dfn>, which may be null.
</p>
<p class="issue">
The following paragraph can be removed once the behavior change lands in
[[input-events]].
</p>
<p>
When an [=EditContext editing host=] receives text input from the [=Text Input
Service=], as the <a href=
"https://www.w3.org/TR/uievents/#default-action">default action</a> for the
<a href=
"https://www.w3.org/TR/uievents/#event-type-beforeinput">beforeinput</a> event
fired as a result of that input the user agent must run [=Handle Input for
EditContext=] given the [=EditContext editing host=] .
</p>
<h4 id="edit-context-differences">
Differences for an EditContext editing host
</h4>
<div>
<p>
In many ways, an <a>EditContext editing host</a> behaves in the same way as
other types of [=editing host=], e.g. for a [^html-global/contenteditable^]
element. Notable similarities include:
</p>
<ul>
<li>Each child node of the <a>EditContext editing host</a> becomes <a href=
"https://w3c.github.io/editing/docs/execCommand/#editable">editable</a>, unless
that node has a [^html-global/contenteditable^] attribute set to
"<code>false</code>".
</li>
<li>The user agent handles focus and caret navigation for any editable element
in the <a>EditContext editing host</a>.
</li>
<li>The <a>EditContext editing host</a> receives key events and the <a href=
"https://www.w3.org/TR/uievents/#event-type-beforeinput">beforeinput</a> event
as specified in [[uievents]].
</li>
</ul>
<p>
There are also some ways that an <a>EditContext editing host</a> differs from
other types of [=editing hosts=]:
</p>
<ul>
<li>When the {{Document}} being edited has an [=active EditContext=], the user
agent must not update the DOM as a direct result of a user action in the
<a>EditContext editing host</a> (e.g., keyboard input in an editable region,
deleting or formatting text, ...).
</li>
<li>When the {{Document}} being edited has an [=active EditContext=], the user
agent must not fire the <a href=
"https://www.w3.org/TR/uievents/#event-type-input">input</a> event against the
<a>EditContext editing host</a> as a direct result of user action event as
specified in [[uievents]].
</li>
</ul>
</div>
<h4>
EditContext events
</h4>
<p>
The user agent fires several types of events against the {{EditContext}} in
order to inform the author when they must update the state of the DOM in
response to changes from the [=Text Input Service=], or respond to a query from
the [=Text Input Service=]. Since the timings of [=Text Input Service=]s are
platform-specific, authors should avoid taking dependencies on the timing of
these events.
</p>
<ul>
<li>The user agent must fire {{TextUpdateEvent}} when the [=Text Input
Service=] indicates that the user has made changes to the text, the selection,
or the composition range properties of the EditContext. When the author
receives this event, they must render the changes back to the page's view so
the user can see what they are typing.
</li>
<li>The user agent must fire {{TextFormatUpdateEvent}} when the [=Text Input
Service=] indicates that certain formats should be applied to the text being
composed. When the author receives this event, they must render the formatting
change back to the page's view to aid the user with their IME composition.
</li>
<li>
<p>
The user agent must fire {{CharacterBoundsUpdateEvent}} when the [=Text Input
Service=] indicates that it requires character bounds information to support
the [=Text Input Method=] in properly displaying its user interface. After
receiving {{CharacterBoundsUpdateEvent}}, the author must compute the requested
character bounds and call {{EditContext/updateCharacterBounds}} to update the
character bounds in the EditContext's [=text state=]. The author should perform
the {{EditContext/updateCharacterBounds}} call synchronously within the
{{CharacterBoundsUpdateEvent}} event handler if possible; if not, it is
permissible to call it asynchronously. Upon receiving
{{EditContext/updateCharacterBounds}}, the user agent must pass the character
bounds information on to the [=Text Input Service=].
</p>
<p class="note">
The longer the author delays the {{EditContext/updateCharacterBounds}} call,
the higher the likelihood that the user will observe a visual stutter as the
IME window repositions itself in the middle of a composition.
</p>
</li>
</ul>
<h4>
Event loop changes
</h4>
<p>
A new step will be introduced as a substep within the [=Update the rendering=]
step in the HTML Event Loops Processing Model, immediately following step 15
(which runs the focusing steps for {{Document}}s whose <a href=
"https://html.spec.whatwg.org/#focused-area-of-the-document">focused area</a>s
become non-focusable). The step is: For each <a href=
"https://html.spec.whatwg.org/multipage/document-sequences.html#fully-active">fully
active</a> {{Document}} |doc|, [=queue a global task=] on the [=DOM
manipulation task source=] given |doc|'s [=relevant global object=] to run the
[=Update the Text Edit Context=] steps given |doc|.
</p>
<section id="examples" class="informative">
<h4>
Examples
</h4>
<p>
Using an {{EditContext}}, an author can mark a region of the document editable
by <a data-lt="associated element">associating</a> an {{EditContext}} object
with an element as shown in the example below:
</p>
<aside class="example" title="Associate an EditContext with an Element">
<pre><script type="module">
let canvas = document.querySelector("canvas")
canvas.editContext = new EditContext()
// When the associated element is focused, the EditContext is automatically activated.
canvas.focus();
</script>
<canvas></canvas></pre>
</aside>
<p>
In the example below, the author is using a canvas to draw an editable region
that allows the user to input a single line of text rendered with a monospace
font. The text for the editable region is maintained by the author as a String.
The text offsets for the selection in the editable region are maintained by the
author as a pair of Numbers: selectionStart and selectionEnd. The Numbers refer
to the count of the number of UTF-16 codepoints to the left of the start and
end of the selection respectively. For the sake of communicating the bounding
boxes for the current selection and the editable region of the document to Text
Input Services, the author also computes the bounding rectangle in CSS pixels
for the selection and the editable region of the document. The offset of the
rectangle is expressed relative to the origin of the canvas element since that
is the element to which the author has <a data-lt=
"associated element">associated</a> an EditContext. Since the model for the
author’s representation of text and selection location matches the form
expected by the EditContext API, the author can simply assign those properties
to the EditContext <a data-lt="associated element">associated</a> with the
canvas whenever those values change.
</p>
<aside class="example" title=
"Using EditContext with editing model, view, and controller">
<pre><script type="module">
// This example is built on top of example 1.
// Only the added logic is shown here for brevity.
class EditingModel {
constructor(text, selectionStart, selectionEnd) {
this.text = text
this.selectionStart = selectionStart
this.selectionEnd = selectionEnd
}
}
class EditingView {
constructor(canvas, model) {
this.canvas = canvas
this.model = model
}
render() {
// render the text
let canvasContext2D = this.canvas.getContext("2d");
canvasContext2D.strokeText(this.model.text);
// render the selection (implementation omitted for brevity)
}
computeSelectionBound() {
// implementation omitted for brevity
}
computeControlBound() {
// implementation omitted for brevity
}
}
class EditingController {
constructor(model, view, editContext) {
this.view = view
this.model = model
this.editContext = editContext
}
render() {
view.render()
// keep EditContext in sync, which essentially means
// rendering the plain text view of the model.
let editContext = this.canvas.editContext
this.editContext.updateText(0, this.model.text.length, this.model.text)
this.editContext.updateSelection(this.model.selectionStart, this.model.selectionEnd)
let selectionBounds = view.computeSelectionBound()
let controlBounds = view.computeControlBound()
// These bounds have x, y, width and height members
// so they can be assigned directly to EditContext.
editContext.updateSelectionBounds(selectionBounds)
editContext.updateControlBounds(controlBounds)
}
}
let canvas = document.querySelector("canvas")
canvas.editContext = new EditContext()
let editingModel = new EditingModel("", 0, 0, 0, 0)
let editingView = new EditingView(canvas, editingModel)
let editingController = new EditingController(editingModel,
editingView, canvas.editContext);
editingController.render()
</script>
<canvas></canvas></pre>
</aside>
<p>
Building on the previous example, in response to user input, authors should
handle the events of both the editable element (in this case a canvas) and the
EditContext.
</p>
<p>
Input events against the DOM continue to describe the user’s intent
</p>
<p>
The below example shows how to handle {{TextUpdateEvent}},
{{TextFormatUpdateEvent}}, and {{CharacterBoundsUpdateEvent}} to update the
model and render the result to the canvas.
</p>
<aside class="example" title=
"Event handlers for TextUpdateEvent, TextFormatUpdateEvent, and CharacterBoundsUpdateEvent">
<pre><script>
// This example is built on top of example 1 and example 2.
// Only the added logic is shown here for brevity.
class EditingModel {
updateText(updateRangeStart, updateRangeEnd, updateText) {
this.text = this.text.substring(0, updateRangeStart) + updateText
+ this.text.substring(updateRangeEnd)
}
updateSelection(selectionStart, selectionEnd) {
this.selectionStart = selectionStart
this.selectionEnd = selectionEnd
}
updateTextFormats(textFormats) {
this.textFormats = textFormats
}
}
class EditingView {
render() {
// render the text (implementation omitted for brevity)
// render the selection (implementation omitted for brevity)
// render the IME decoration
this.model.textFormats.forEach( textFormat => {
// For brevity, these variables' initialization are omitted:
// anchorX: the x coordinate of the beginning of the string
// lineY: the y coordinate of the underline
// charWidth: the width of the character (here we are using a mono-spaced font)
// thickWidth/thinWidth: pre-defined width for thick/thin lines.
let lineStartX = anchorX + textFormat.rangeStart * charWidth;
let lineEndX = anchorX + textFormat.rangeEnd * charWidth;
canvasContext2D.lineWidth = (textFormat.underlineThickness == 'Thick')?
thickWidth : thinWidth;
canvasContext2D.beginPath();
canvasContext2D.moveTo(lineStartX, lineY);
canvasContext2D.lineTo(lineEndX, lineY);
canvasContext2D.stroke();
})
}
computeCharacterBounds(rangeStart, rangeEnd) {
// implementation omitted for brevity
}
}
class EditingController {
handleTextUpdate(updateRangeStart, updateRangeEnd, text,
selectionStart, selectionEnd) {
this.model.updateText(updateRangeStart, updateRangeEnd, text)
this.model.updateSelection(selectionStart, selectionEnd)
}
handleTextFormatUpdate(textFormats) {
this.model.updateTextFormats(textFormats);
}
handleCharacterBoundsUpdate(rangeStart, rangeEnd) {
characterBounds = this.view.computeCharacterBounds(rangeStart, rangeEnd);
this.editContext.updateCharacterBounds(rangeStart, characterBounds);
}
}
// When the user is typing, EditContext will receive textupdate events,
// which can be used to update the editor's model.
editContext.addEventListener("textupdate", e => {
editingController.handleTextUpdate(e.updateRangeStart, e.updateRangeEnd, e.text,
e.selectionStart, e.selectionEnd)
});
// EditContext will also receive textformatupdate event for IME decoration.
// Ex. thin/thick underline for the "phrase mode" in Japanese IME.
editContext.addEventListener("textformatupdate", e => {
editingcontroller.handleTextFormatUpdate(e.getTextFormats());
});
// When receiving CharacterBoundsUpdate event, the author is responsible to compute
// the bounds of characters from rangeStart to rangeEnd, and call
// EditContext.updateCharacterBounds to update the character bounds in EditContext.
editContext.addEventListener("characterboundsupdate", e => {
editingcontroller.handleCharacterBoundsUpdate(e.rangeStart, e.rangeEnd);
});
</script></pre>
</aside>
</section>
</section>
<section id="interactions" class="informative">
<h3>
Interactions with Other Editing Primitives
</h3>
<p>
An author doesn’t have to use a canvas element with an EditContext. In the
example below the author uses a div to establish an editable region of the
document and renders the contents into that editable region using various other
styled elements, images and text. This allows the author to leverage other
built-in editing primitives from the user agent such as selection and
spellcheck.
</p>
<aside class="example" title=
"How native selection can be leveraged to handle caret navigation.">
<pre><div></div>
<script>
// This example reuses EditModel and EditController in Example 2 and 3.
let div = document.querySelector("div")
div.editContext = new EditContext()
div.focus();
class EditingView {
constructor(div, model) {
this.div = div
this.model = model
}
render() {
// render the text
this.div.innerText = this.model.text
// render the selection (implementation omitted for brevity)
}
computeSelectionBound() {
// implementation omitted for brevity
}
computeControlBound() {
// implementation omitted for brevity
}
computeCharacterBounds(rangeStart, rangeEnd) {
// implementation omitted for brevity
}
}
class EditingController {
handleSelectionChange() {
// Authors are responsible to map the selection from the DOM space to the
// plain text space. One approach is to use range.toString() to get the plain text
// before the selection start/end, and use the text length as the selection index.
let s = document.getSelection()
let range = new Range()
range.setEnd(s.anchorNode, s.anchorOffset)
range.setStartBefore(parentContainer)
let selectionStart = range.toString().length
range.setEnd(s.focusNode, s.focusOffset)
range.setStartBefore(parentContainer)
let selectionEnd = range.toString().length
// Update model
this.model.updateSelection(selectionStart, selectionEnd)
this.render()
}
}
document.addEventListener("selectionchange", e => {
editingController.handleSelectionChange()
});
</script></pre>
</aside>
<aside class="example" title=
"How beforeinput can be used to catch insertReplacementText to apply spelling changes">
<pre><script>
// This example is built on top of example 4.
// Only the added logic is shown here for brevity.
class EditingController {
handleSpellCheck(newText, range) {
let updateRangeStart = range.startOffset
let updateRangeEnd = range.endOffset
// Update model
this.model.updateText(updateRangeStart, updateRangeEnd, newText)
let newCaretPosition = updateRangeStart + newText.length
this.model.updateSelection(newCaretPosition, newCaretPosition)
this.render()
}
}
div.spellcheck = true;
div.addEventListener("beforeinput", e => {
if (e.inputType === "insertReplacementText") { // for spellcheck
let newText = e.dataTransfer.getData("text");
let range = e.getTargetRanges()[0];
editingController.handleSpellCheck(newText, range)
}
})
</script></pre>
</aside>
<aside class="example" title=
"How beforeinput can be used to catch deleteByDrag and insertFromDrop to apply drag and drop changes">
<pre><script>
// This example is built on top of example 4.
// Only the added logic is shown here for brevity.
class EditingController {
handleDeleteByDrag() {
// Update model
this.model.updateText(this.model.selectionStart, this.model.selectionEnd, "")
this.render()
}
handleInsertFromDrop(newText, caretPosition) {
// Update model
editingModel.updateText(caretPosition, caretPosition, newText)
editingModel.updateSelection(caretPosition, caretPosition + newText.length)
this.render()
}
}
div.addEventListener("beforeinput", e => {
if (e.inputType === "deleteByDrag") {
editingController.handleDeleteByDrag()
}
if (e.inputType === "insertFromDrop") {
newText = e.dataTransfer.getData('text/plain');
let selection = document.getSelection();
let caretPosition = selection.anchorOffset;
editingController.handleInsertFromDrop(newText, caretPosition)
}
})
</script></pre>
</aside>
</section>
</section>
<section id="conformance">
<p>
This specification defines conformance criteria that apply to a single product:
the user agent that implements the interfaces that it contains.
</p>
<p>
Conformance requirements phrased as algorithms or specific steps may be
implemented in any manner, so long as the end result is equivalent. (In
particular, the algorithms defined in this specification are intended to be
easy to follow, and not intended to be performant.)
</p>
</section>
<section data-dfn-for="EditContext">
<h2>
EditContext API
</h2>
<section data-dfn-for="Element">
<h3>
Extensions to the HTMLElement interface
</h3>
<pre class="idl">
partial interface HTMLElement {
attribute EditContext? editContext;
};
</pre>
<p>
An {{HTMLElement}} has an internal slot [[\EditContext]], which is a reference
to an {{EditContext}} and is intially null.
</p>
<dl>
<dt>
editContext
</dt>
<dd>
The {{HTMLElement/editContext}} getter steps are to return the value of
[=this=]'s internal [[\EditContext]] slot.
</dd>
<dd>
The {{HTMLElement/editContext}} setter must follow these steps:
<div class="algorithm">
<dl>
<dt>
Input
</dt>
<dd>
|editContext|
</dd>
<dt>
Output
</dt>
<dd>
None
</dd>
</dl>
<ol>
<li>If [=this=]'s [=Element/local name=] is neither a [=valid shadow host
name=] nor "<code>canvas</code>", then [=exception/throw=] a
{{"NotSupportedError"}} {{DOMException}}.
</li>
<li>If |editContext| is not null, then:
<ol>
<li>If |editContext|'s <a>associated element</a> is equal to [=this=], then
terminate these steps.
</li>
<li>If |editContext|'s <a>associated element</a> is not null, then
[=exception/throw=] a {{"NotSupportedError"}} {{DOMException}}.
</li>
<li>Set |editContext|'s <a>associated element</a> to [=this=].
</li>
</ol>
</li>
<li>Let |oldEditContext| be the value of [=this=]'s internal [[\EditContext]]
slot.
</li>
<li>If |oldEditContext| is not null, then:
<ol>
<li>[=Assert=]: |oldEditContext|'s <a>associated element</a> is equal to
[=this=].
</li>
<li>Set |oldEditContext|'s <a>associated element</a> to null.
</li>
</ol>
</li>
<li>Set [=this=]'s internal [[\EditContext]] slot to be |editContext|.
</li>
<li>If |oldEditContext| is not null and |oldEditContext| is [=this=]'s <a href=
"https://dom.spec.whatwg.org/#concept-node-document">node document</a>'s
[=active EditContext=], then run the steps to [=deactivate an EditContext=]
with |oldEditContext|.
</li>
</ol>
</div><!-- algorithm -->
</dd>
</dl>
<h4>
<dfn class="export">Handle input for EditContext</dfn>
</h4>
<div class="algorithm">
<dl>
<dt>
Input
</dt>
<dd>
|element|, the {{HTMLElement}} receiving the input
</dd>
<dt>
Output
</dt>
<dd>
None
</dd>
</dl>
<ol>
<li>Let |editContext| be |element|'s <a href=
"https://dom.spec.whatwg.org/#concept-node-document">node document</a>'s
[=active EditContext=]
</li>
<li>If |editContext| is null, return.
</li>
<li>
<p>
Run the steps to [=Update the EditContext=] given |editContext| and the [=Text
Edit Context=]'s [=text state=]'s [=text=], [=text formats=], [=selection
start=], [=selection end=], [=is composing=], [=composition start=], and
[=composition end=].
</p>
<p class="note">
Since [=Text Edit Context=] is an abstraction over the common aspects of text
input across different operating systems, the determination of the values in
the [=Text Edit Context=] is explicitly not given in this specification. They
will vary across different operating systems and input devices.
</p>
</li>
</ol>
</div><!-- algorithm -->
<h4>
<dfn>EditContext-handled inputType</dfn>
</h4>
<div class="algorithm">
An <a href=
"https://www.w3.org/TR/uievents/#dom-inputevent-inputtype">inputType</a> is an
[=EditContext-handled inputType=] if it is one of the following:
<ul>
<li>
<code>insertText</code>
</li>
<li>
<code>insertTranspose</code>
</li>
<li>
<code>deleteWordBackward</code>
</li>
<li>
<code>deleteWordForward</code>
</li>
<li>
<code>deleteContent</code>
</li>
<li>
<code>deleteContentBackward</code>
</li>
<li>
<code>deleteContentForward</code>
</li>
</ul>
<div class="note">
The <a href=
"https://www.w3.org/TR/uievents/#dom-inputevent-inputtype">inputType</a>s
handled by {{EditContext}} are those which operate only on raw text. Other