This document is a preliminary draft of a specification for the Selection API and selection related functionality. It replaces a couple of old sections of the HTML specification, the selection part of the old DOM Range specification.
This document defines APIs for selection, which allows users and authors to select a portion of a document or specify a point of interest for copy, paste, and other editing operations.
This is work in progress.
IE9 and Firefox 6.0a2 allow arbitrary ranges in the selection, which follows what this spec originally said. However, this leads to unpleasant corner cases that authors, implementers, and spec writers all have to deal with, and they don't make any real sense. Chrome 14 dev and Opera 11.11 aggressively normalize selections, like not letting them lie inside empty elements and things like that, but this is also viewed as a bad idea, because it takes flexibility away from authors.
So I changed the spec to a made-up compromise that allows some simplification but doesn't constrain authors much. See discussion. Basically it would throw exceptions in some places to try to stop the selection from containing a range that had a boundary point other than an Element or Text node, or a boundary point that didn't descend from a Document.
But this meant getRangeAt() had to start returning a copy, not a reference. Also, it would be prone to things failing weirdly in corner cases. Perhaps most significantly, all sorts of problems might arise when DOM mutations transpire, like if a boundary point's node is removed from its parent and the mutation rules would place the new boundary point inside a non-Text/Element node. And finally, the previously-specified behavior had the advantage of matching two major implementations, while the new behavior matched no one. So I changed it back.
See bug 15470. IE9, Firefox 12.0a1, Chrome 17 dev, and Opera Next 12.00 alpha all make the range initially null.
Every document with a [=Document/browsing context=] has a unique selection associated with it.
This is a requirement of the HTML spec. IE9 and Opera Next 12.00 alpha seem to follow it, while Firefox 12.0a1 and Chrome 17 dev seem not to. See Mozilla bug, WebKit bug.
This one selection must be shared by all the content of the document (though not by nested documents), including any [=editing hosts=] in the document.
Each selection can be associated with a single range. When there is no range associated with the selection, the selection is empty. The selection must be initially empty.
A document's selection is a singleton object associated
with that document, so it gets replaced with a new object when
Document.open() is called. See bug 15470.
IE9 and Opera Next 12.00 alpha allow the user to reset the range to
null after the fact by clicking somewhere; Firefox 12.0a1 and Chrome 17
dev do not. We follow Gecko/WebKit, because it lessens the chance of
getRangeAt(0) throwing.
Once a selection is associated with a given range, it must continue to be associated with that same range until this specification requires otherwise.
For instance, if the DOM changes in a way that changes the range's boundary points, or a script modifies the boundary points of the range, the same range object must continue to be associated with the selection. However, if the user changes the selection or a script calls {{addRange()}}, the selection must be associated with a new range object, as required elsewhere in this specification.
If the selection's range is not null and is [=range/collapsed=], then the caret position must be at that range's boundary point. When the selection is not [=range/collapsed=], this specification does not define the caret position; user agents should follow platform conventions in deciding whether the caret is at the start of the selection, the end of the selection, or somewhere else.
Each selection has a direction: forwards, backwards, or directionless. If the user creates a selection by indicating first one boundary point of the range and then the other (such as by clicking on one point and dragging to another), and the first indicated boundary point is [=boundary point/after=] the second, then the corresponding selection must initially be backwards. If the first indicated boundary point is [=boundary point/before=] the second, then the corresponding selection must initially be forwards. Otherwise, it must be directionless.
When the selection's range is mutated by scripts, e.g. via {{Range/selectNode(node)}}, direction of the selection must be preserved.
Each selections also have an anchor and a focus. If the selection's range is null, its anchor and focus are both null. If the selection's range is not null and its direction is forwards, its anchor is the range's [=range/start=], and its focus is the [=range/end=]. Otherwise, its focus is the [=range/start=] and its anchor is the [=range/end=].
anchor and focus of selection need not to be in the [=document tree=]. It could be in a [=shadow tree=] of the same [=document=].
Each document, input element, and textarea element has a boolean has scheduled selectionchange event, which is initially false.
Selection interface provides a way to interact with the selection associated with each document.
[Exposed=Window]
interface Selection {
readonly attribute Node? anchorNode;
readonly attribute unsigned long anchorOffset;
readonly attribute Node? focusNode;
readonly attribute unsigned long focusOffset;
readonly attribute boolean isCollapsed;
readonly attribute unsigned long rangeCount;
readonly attribute DOMString type;
readonly attribute DOMString direction;
Range getRangeAt(unsigned long index);
undefined addRange(Range range);
undefined removeRange(Range range);
undefined removeAllRanges();
undefined empty();
sequence<StaticRange> getComposedRanges(optional GetComposedRangesOptions options = {});
undefined collapse(Node? node, optional unsigned long offset = 0);
undefined setPosition(Node? node, optional unsigned long offset = 0);
undefined collapseToStart();
undefined collapseToEnd();
undefined extend(Node node, optional unsigned long offset = 0);
undefined setBaseAndExtent(Node anchorNode, unsigned long anchorOffset, Node focusNode, unsigned long focusOffset);
undefined selectAllChildren(Node node);
undefined modify(optional DOMString alter, optional DOMString direction, optional DOMString granularity);
[CEReactions] undefined deleteFromDocument();
boolean containsNode(Node node, optional boolean allowPartialContainment = false);
stringifier;
};
dictionary GetComposedRangesOptions {
sequence<ShadowRoot> shadowRoots = [];
};
The attribute must return the anchor [=boundary point/node=] of [=this=], or `null` if the anchor is null or anchor is not in the [=document tree=].
The attribute must return the anchor [=boundary
point/offset=] of [=this=], or 0 if the anchor
is null or anchor is not in the [=document tree=].
The attribute must return the focus [=boundary point/node=] of [=this=], or `null` if the focus is null or focus is not in the [=document tree=].
The attribute must return the focus [=boundary
point/offset=] of [=this=], or 0 if the focus
is null or focus is not in the [=document tree=].
The attribute must return true if and only if the anchor and focus are the same (including if both are null). Otherwise it must return false.
The attribute must return 0 if [=this=] is
empty or either focus or anchor is not in the
[=document tree=], and must return 1 otherwise.
The attribute must return `"None"` if [=this=] is empty or either focus or anchor is not in the [=document tree=], `"Caret"` if [=this=]'s range is [=range/collapsed=], and `"Range"` otherwise.
The attribute must return `"none"` if [=this=] is empty or this selection is directionless. `"forward"` if this selection's direction is forwards and `"backward"` if this selection's direction is backwards.
The method must throw an {{IndexSizeError}} exception if
index is not 0, or if [=this=] is
empty or either focus or anchor is not in the
[=document tree=]. Otherwise, it must return a reference to (not a
copy of) [=this=]'s range.
Thus subsequent calls of this method returns the same range
object if nothing has removed [=this=]'s range in the meantime. In
particular, getSelection().getRangeAt(0) ===
getSelection().getRangeAt(0) evaluates to true
if the selection is not empty.
The method must follow these steps:
rangeCount is not 0, abort these
steps.
Since range is added by reference, subsequent calls to
getRangeAt(0) returns the same object, and any changes
that a script makes to range after it is added must be
reflected in the selection, until something else removes or
replaces [=this=]'s range. In particular, the
selection will contain b as opposed to
a after running the following code: var r =
document.createRange(); r.selectNode(a);
getSelection().addRange(r); r.selectNode(b);
The method must make [=this=] empty by disassociating its range if [=this=]'s range is range. Otherwise, it must throw a {{NotFoundError}}.
The method must make [=this=] empty by disassociating its range if [=this=] has an associated range.
The method must be an alias, and behave identically, to
removeAllRanges().
The method must follow these steps:
removeAllRanges() and abort these steps.
The method must be an alias, and behave identically, to
collapse().
The method must throw {{InvalidStateError}} exception if the [=this=] is empty. Otherwise, it must create a new range, [=Range/set the start=] both its [=range/start=] and [=range/end=] to the [=range/start=] of [=this=]'s range, and then set [=this=]'s range to the newly-created range.
For collapseToStart/End, IE9 mutates the existing range, while Firefox 9.0a2 and Chrome 15 dev replace it with a new one. The spec follows the majority and replaces it with a new one, leaving the old Range object unchanged.
The method must throw {{InvalidStateError}} exception if the [=this=] is empty. Otherwise, it must create a new range, [=Range/set the start=] both its [=range/start=] and [=range/end=] to the [=range/end=] of [=this=]'s range, and then set [=this=]'s range to the newly-created range.
The method must follow these steps:
Reverse-engineered circa January 2011. IE doesn't support it, so I'm relying on Firefox (implemented extend() sometime before 2000) and WebKit (implemented extend() in 2007). I'm mostly ignoring Opera, because gsnedders tells me its implementation isn't compatible. Firefox 12.0a1 seems to mutate the existing range. IE9 doesn't support extend(), and it's impossible to tell whether Chrome 17 dev or Opera Next 12.00 alpha mutate or replace, because getRangeAt() returns a copy anyway. Nevertheless, I go against Gecko here, to be consistent with collapse().
The method must follow these steps:
The method must follow these steps:
0).
Based mostly on Firefox 9.0a2. It has a bug that I didn't reproduce, namely that if you pass a Document as the argument, the end offset becomes 1 instead of the number of children it has. It also throws a RangeException instead of DOMException, because its implementation predated their merging.
IE9 behaves similarly but with glitches. It throws "Unspecified error." if the node is detached or display:none, and apparently in some random other cases too. It throws "Invalid argument." for detached comments (only!). Finally, if you pass it a comment, it seems to select the whole comment, unlike with text nodes.
Chrome 16 dev behaves as you'd expect given its Selection implementation. It refuses to select anything that's not visible, so it's almost always wrong. Opera 11.50 just does nothing in all my tests, as usual.
The new range replaces any existing one, doesn't mutate it. This matches IE9 and Firefox 12.0a1. (Chrome 17 dev and Opera Next 12.00 alpha can't be tested, because getRangeAt() returns a copy anyway.)
The method must follow these steps:
We need to more precisely define what it means to extend or move selection by each granularity.
The method must invoke {{Range/deleteContents()}} on [=this=]'s range if [=this=] is not empty and both focus and anchor are in the [=document tree=]. Otherwise the method must do nothing.
This is the one method that actually mutates the range instead of replacing it. This matches IE9 and Firefox 12.0a1. (Chrome 17 dev and Opera Next 12.00 alpha can't be tested, because getRangeAt() returns a copy anyway.)
The method must return false if [=this=] is
empty or if node's [=tree/root=] is not the
document associated with [=this=].
Otherwise, if allowPartialContainment is
false, the method must return true if and
only if [=range/start=] of its range is [=boundary
point/before=] or visually equivalent to the first boundary
point in the node and [=range/end=]
of its range is [=boundary point/after=] or visually
equivalent to the last boundary point in the
node.
If allowPartialContainment is true, the
method must return true if and only if [=range/start=]
of its range is [=boundary point/before=] or visually
equivalent to the last boundary point in the node
and [=range/end=] of its range is
[=boundary point/after=] or visually equivalent to the first
boundary point in the node.
The stringification must return the string, which is the concatenation of the rendered text if there is a [=range=] associated with [=this=].
If the selection is within a textarea or input element, it must return the selected substring in its value.
See also nsISelection.idl from Gecko. This spec doesn't have everything from there yet, in particular selectionLanguageChange() and containsNode() are missing. They are missing because I couldn't work out how to define them in terms of Ranges.
Originally, the Selection interface was a Netscape feature. The original implementation was carried on into Gecko (Firefox), and the feature was later implemented independently by other browser engines. The Netscape implementation always allowed multiple ranges in a single selection, for instance so the user could select a column of a table However, multi-range selections proved to be an unpleasant corner case that web developers didn't know about and even Gecko developers rarely handled correctly. Other browser engines never implemented the feature, and clamped selections to a single range in various incompatible fashions.
This specification follows non-Gecko engines in restricting
selections to at most one range, but the API was still originally
designed for selections with arbitrary numbers of ranges. This
explains oddities like the coexistence of removeRange()
and removeAllRanges(), and a getRangeAt()
method that takes an integer argument that must always be zero.
All of the members of the {{Selection}} interface are defined in terms
of operations on the range object (if any)
represented by the object. These operations can raise exceptions, as
defined for the {{Range}} interface; this can therefore result in the
members of the Selection interface raising exceptions as well,
in addition to any explicitly called out above.
This specification extends several interfaces to provide entry points to the interfaces defined in this specification.
Document interface
The Document
interface is defined in [[HTML]].
partial interface Document {
Selection? getSelection();
};
The method must return the selection associated with [=this=] if [=this=] has an associated [=Document/browsing context=], and it must return `null` otherwise.
The Window interface is
defined in [[HTML]].
partial interface Window {
Selection? getSelection();
};
The method must invoke and return the result of {{Document/getSelection()}} on [=this=]'s {{Window.document}} attribute.
The GlobalEventHandlers
interface is defined in [[HTML]].
partial interface mixin GlobalEventHandlers {
attribute EventHandler onselectstart;
attribute EventHandler onselectionchange;
};
The attribute must be an event handler IDL attribute for the selectstart event supported by all HTML elements, {{Document}} objects, and {{Window}} objects.
The attribute must be an event handler IDL attribute for the selectionchange event supported by all HTML elements, {{Document}} objects, and {{Window}} objects.
When the user agent is to [=replace data=] or [=CharacterData/substring data=] on {{CharacterData}}, the user agent must update the range associated with selection of the [=Node/node document=] of the {{CharacterData}} as if it's a live range.
When the user agent is to split a {{Text}} [=node=], the user agent must update the range associated with selection of the [=Node/node document=] of the {{Text}} as if it's a live range.
When the user agent is to run steps for normalize()
method, the user agent must update the range associated with
selection of the [=Node/node document=] of [=this=] as if it's a
live range.
When the user agent is to [=remove=] or [=insert=] a [=node=], the user agent must update the range associated with selection of the [=Node/node document=] of the [=node=] as if it's a live range.
The user agent should allow the user to change the selection associated with the [=navigable/active document=]. If the user makes any modification to a selection, the user agent must create a new range with suitable [=range/start=] and [=range/end=] of the range and associate the selection with this new range (not modify the existing range), and set update selection's direction to forwards if the [=range/start=] is [=boundary point/before=] or equal to the [=range/end=], backwards if if the [=range/end=] is [=boundary point/before=] the [=range/start=], or directionless if the [=range/start=] and the [=range/end=] cannot be ordered due to the platform convention.
The user agent must not make a selection empty if it was not already empty in response to any user actions (e.g. clicking on a non-editable region).
See bug 15470. IE9 and Opera Next 12.00 alpha allow the user to reset the range to null after the fact by clicking somewhere; Firefox 12.0a1 and Chrome 17 dev do not. I follow Gecko/WebKit, because it lessens the chance of getRangeAt(0) throwing.
selectstart event
When the user agent is about to associate a new range
newRange to the selection in response to a user
initiated action, the user agent must fire an event named
selectstart, which bubbles and is cancelable, at the
[=boundary point/node=] associated with the boundary point of
newRange's [=range/start=] prior to changing the selection
if the selection was previously empty or the previously
associated range was [=range/collapsed=].
If the event is canceled, the user agent must not change the selection.
The user agent must not fire an event when the user agent sets the selection empty.
selectionchange event
When the selection is dissociated with its range, associated with a new range, or the associated range's boundary point is mutated either by the user or the content script, the user agent must schedule a selectionchange event on document.
When an [^input^] or [^textarea^] element provide a text selection and its selection changes (in either extent or [=direction=]), the user agent must schedule a selectionchange event on the element.
selectionhange event
To schedule a selectionchange event on a node target, run these steps:
selectionhange event
To fire a selectionchange event on a node target, run these steps:
selectionchange, which bubbles and not cancelable, at
target.
selectionchange, which does not bubble
and not cancelable, at target.
This specification defines conformance criteria that apply to a single product: the user agent that implements the interfaces that it contains.
There are no known security considerations for this standard.
To mitigate potential privacy risks of exposing user's use of assistive technologies, for example, user agent may elect to emulate mouse and keyboard events typically associated with selectstart or selectionchange events when the user opts to modify the selection of a document.
Many thanks to