W3C

CSSOM View Module

W3C Working Draft,

This version:
http://www.w3.org/TR/2016/WD-cssom-view-1-20160317/
Latest version:
http://www.w3.org/TR/cssom-view-1/
Editor's Draft:
https://drafts.csswg.org/cssom-view/
Previous Versions:
http://www.w3.org/TR/2013/WD-cssom-view-20131217/
http://www.w3.org/TR/2011/WD-cssom-view-20110804/
http://www.w3.org/TR/2009/WD-cssom-view-20090804/
http://www.w3.org/TR/2008/WD-cssom-view-20080222/
http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/
Feedback:
www-style@w3.org with subject line “[cssom-view] … message topic …” (archives)
Test Suite:
http://test.csswg.org/suites/cssom-view-1_dev/nightly-unstable/
Issue Tracking:
Inline In Spec
Editor:
(Opera Software ASA)
Former Editors:
Glenn Adams (Cox Communications, Inc.)
Anne van Kesteren (Opera Software ASA)
Issues list:
Bugzilla (file a bug)

Abstract

The APIs introduced by this specification provide authors with a way to inspect and manipulate the visual view of a document. This includes getting the position of element layout boxes, obtaining the width of the viewport through script, and also scrolling an element.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, in speech, etc.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

The (archived) public mailing list www-style@w3.org (see instructions) is preferred for discussion of this specification. When sending e-mail, please put the text “cssom-view” in the subject, preferably like this: “[cssom-view] …summary of comment…

This document was produced by the CSS Working Group (part of the Style Activity).

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 1 September 2015 W3C Process Document.

1. Background

Many of the features defined in this specification have been supported by browsers for a long period of time. The goal of this specification is to define these features in such a way that they can be implemented by all browsers in an interoperable manner. The specification also defines a couple of new features that will hopefully be useful to authors. (If they are not you can bug us!)

2. Terminology

Terminology used in this specification is from DOM, CSSOM and HTML. [DOM] [CSSOM] [HTML]

The HTML body element#the-html-body-elementReferenced in:2. Terminology5. Extensions to the Document Interface (2) (3) (4)6. Extensions to the Element Interface (2) (3) (4) (5) (6) (7) (8) (9)7. Extensions to the HTMLElement Interface (2) (3) (4) is the first body HTML element child of the root HTML element html.

Content edge, padding edge#padding-edgeReferenced in:2. Terminology (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)6. Extensions to the Element Interface (2) (3) (4) (5) (6) (7) (8)6.1. Element Scrolling Members (2) (3) (4)7. Extensions to the HTMLElement Interface (2)10. Extensions to the MouseEvent Interface (2), border edge#border-edgeReferenced in:6. Extensions to the Element Interface (2) (3) (4)7. Extensions to the HTMLElement Interface (2) (3) (4) (5) (6)8. Extensions to the HTMLImageElement Interface (2), margin edge#margin-edgeReferenced in:2. Terminology (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16), and viewport#viewportReferenced in:2. Terminology (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15)3.1. Scrolling4. Extensions to the Window Interface (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30)5. Extensions to the Document Interface (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18)6. Extensions to the Element Interface (2) (3) (4) (5) (6) (7) (8) (9) (10)6.1. Element Scrolling Members (2) (3) (4)10. Extensions to the MouseEvent Interface (2)12.1. Resizing viewports12.2. Scrolling (2)12.3. Event summary (2)13.1. Smooth Scrolling: The scroll-behavior Property are defined by CSS.

Elements and viewports have an associated scrolling box#scrolling-boxReferenced in:2. Terminology (2) (3)3.1. Scrolling (2) (3)6. Extensions to the Element Interface (2) (3)6.1. Element Scrolling Members (2) (3)13.1. Smooth Scrolling: The scroll-behavior Property (2) (3) (4) if has a scrolling mechanism or it overflows its content area and the used value of the overflow-x or overflow-y property is hidden. [CSS3-BOX]

An element is potentially scrollable#potentially-scrollableReferenced in:2. Terminology5. Extensions to the Document Interface6. Extensions to the Element Interface (2) (3) (4) (5) (6) (7) if all of the following conditions are true:

Note: An element that is potentially scrollable might not have a scrolling box. For instance, it could have overflow set to auto but not have its content overflowing its content area.

A scrolling box of a viewport or element has two overflow directions#overflow-directionsReferenced in:2. Terminology (2) (3) (4) (5) (6) (7) (8) (9) (10)4. Extensions to the Window Interface (2) (3) (4)6.1. Element Scrolling Members (2) (3) (4), depending on the viewport’s or element’s block flow direction and inline base direction, as follows:

If the block flow direction is top-to-bottom and the inline base direction is left-to-right
If the block flow direction is left-to-right and the inline base direction is left-to-right
Rightward and downward.
If the block flow direction is top-to-bottom and the inline base direction is right-to-left
If the block flow direction is right-to-left and the inline base direction is left-to-right
Leftward and downward.
If the block flow direction is right-to-left and the inline base direction is right-to-left
Leftward and upward.
If the block flow direction is left-to-right and the inline base direction is right-to-left
Rightward and upward.

The term scrolling area#scrolling-areaReferenced in:2. Terminology (2)3.1. Scrolling4. Extensions to the Window Interface (2) (3) (4) (5) (6)6. Extensions to the Element Interface (2) (3) (4) (5) (6) (7) (8)6.1. Element Scrolling Members (2) (3) (4) (5) (6) refers to a box of a viewport or an element that has the following edges, depending on the viewport’s or element’s scrolling box’s overflow directions.

If the overflow directions are… For a viewport For an element
rightward and downward
top edge
The top edge of the initial containing block.
right edge
The right-most edge of the right edge of the initial containing block and the right margin edge of all of the viewport’s descendants' boxes.
bottom edge
The bottom-most edge of the bottom edge of the initial containing block and the bottom margin edge of all of the viewport’s descendants' boxes.
left edge
The left edge of the initial containing block.
top edge
The element’s top padding edge.
right edge
The right-most edge of the element’s right padding edge and the right margin edge of all of the element’s descendants' boxes, excluding boxes that have an ancestor of the element as their containing block.
bottom edge
The bottom-most edge of the element’s bottom padding edge and the bottom margin edge of all of the element’s descendants' boxes, excluding boxes that have an ancestor of the element as their containing block.
left edge
The element’s left padding edge.
leftward and downward
top edge
The top edge of the initial containing block.
right edge
The right edge of the initial containing block.
bottom edge
The bottom-most edge of the bottom edge of the initial containing block and the bottom margin edge of all of the viewport’s descendants' boxes.
left edge
The left-most edge of the left edge of the initial containing block and the left margin edge of all of the viewport’s descendants' boxes.
top edge
The element’s top padding edge.
right edge
The element’s right padding edge.
bottom edge
The bottom-most edge of the element’s bottom padding edge and the bottom margin edge of all of the element’s descendants' boxes, excluding boxes that have an ancestor of the element as their containing block.
left edge
The left-most edge of the element’s left padding edge and the left margin edge of all of the element’s descendants' boxes, excluding boxes that have an ancestor of the element as their containing block.
leftward and upward
top edge
The top-most edge of the top edge of the initial containing block and the top margin edge of all of the viewport’s descendants' boxes.
right edge
The right edge of the initial containing block.
bottom edge
The bottom edge of the initial containing block.
left edge
The left-most edge of the left edge of the initial containing block and the left margin edge of all of the viewport’s descendants' boxes.
top edge
The top-most edge of the element’s top padding edge and the top margin edge of all of the element’s descendants' boxes, excluding boxes that have an ancestor of the element as their containing block.
right edge
The element’s right padding edge.
bottom edge
The element’s bottom padding edge.
left edge
The left-most edge of the element’s left padding edge and the left margin edge of all of the element’s descendants' boxes, excluding boxes that have an ancestor of the element as their containing block.
rightward and upward
top edge
The top-most edge of the top edge of the initial containing block and the top margin edge of all of the viewport’s descendants' boxes.
right edge
The right-most edge of the right edge of the initial containing block and the right margin edge of all of the viewport’s descendants' boxes.
bottom edge
The bottom edge of the initial containing block.
left edge
The left edge of the initial containing block.
top edge
The top-most edge of the element’s top padding edge and the top margin edge of all of the element’s descendants' boxes, excluding boxes that have an ancestor of the element as their containing block.
right edge
The right-most edge of the element’s right padding edge and the right margin edge of all of the element’s descendants' boxes, excluding boxes that have an ancestor of the element as their containing block.
bottom edge
The element’s bottom padding edge.
left edge
The element’s left padding edge.

The origin of a scrolling area is the origin of the initial containing block if the scrolling area is a viewport, and otherwise the top left padding edge of the element when the element has its default scroll position. The x-coordinate increases rightwards, and the y-coordinate increases downwards.

The beginning edges#beginning-edgesReferenced in:3.1. Scrolling (2)6.1. Element Scrolling Members (2) of a particular set of edges of a box or element are the following edges:

If the overflow directions are rightward and downward
The top and left edges.
If the overflow directions are leftward and downward
The top and right edges.
If the overflow directions are leftward and upward
The bottom and right edges.
If the overflow directions are rightward and upward
The bottom and left edges.

The ending edges#ending-edgesReferenced in:6.1. Element Scrolling Members (2) of a particular set of edges of a box or element are the following edges:

If the overflow directions are rightward and downward
The bottom and right edges.
If the overflow directions are leftward and downward
The bottom and left edges.
If the overflow directions are leftward and upward
The top and left edges.
If the overflow directions are rightward and upward
The top and right edges.

The term CSS layout box#css-layout-boxReferenced in:2. Terminology (2) (3) (4)6. Extensions to the Element Interface (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15)7. Extensions to the HTMLElement Interface (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)8. Extensions to the HTMLImageElement Interface (2) (3) (4) refers to the same term in CSS. For the purpose of the requirements in this specification, elements that have a computed value of the display property that is table-column or table-column-group must be considered to have an associated CSS layout box (the column or column group, respectively).

The term SVG layout box#svg-layout-boxReferenced in:2. Terminology (2)6. Extensions to the Element Interface refers to the same term in SVG.

The terms CSS layout box and SVG layout box are not currently defined by CSS or SVG.

The term layout box#layout-boxReferenced in:5. Extensions to the Document Interface (2)6. Extensions to the Element Interface (2) refers to either a CSS layout box or an SVG layout box.

The term transforms#transformsReferenced in:5. Extensions to the Document Interface (2) (3) (4) (5)5.1. The CaretPosition Interface6. Extensions to the Element Interface (2) (3) (4) (5) (6)7. Extensions to the HTMLElement Interface (2) (3) (4) (5) (6)8. Extensions to the HTMLImageElement Interface (2)9. Extensions to the Range Interface10. Extensions to the MouseEvent Interface (2)Changes From 4 August 2011 To 17 December 2013 refers to SVG transforms and CSS transforms. [SVG] [CSS-TRANSFORMS-1]

When a method or an attribute is said to call another method or attribute, the user agent must invoke its internal API for that attribute or method so that e.g. the author can’t change the behavior by overriding attributes or methods with custom properties or functions in ECMAScript.

Unless otherwise stated, string comparisons are done in a case-sensitive manner.

2.1. CSS pixels

All coordinates and dimensions for the APIs defined in this specification are in CSS pixels, unless otherwise specified.

Note: This does not apply to e.g. matchMedia() as the units are explicitly given there.

2.2. Zooming

There are two kinds of zoom, page zoom#page-zoomReferenced in:4. Extensions to the Window InterfaceChanges From 4 August 2011 To 17 December 2013 which affects the size of the initial viewport, and pinch zoom#pinch-zoomReferenced in:4. Extensions to the Window InterfaceChanges From 4 August 2011 To 17 December 2013 which acts like a magnifying glass and does not affect the initial viewport or actual viewport. [CSS-DEVICE-ADAPT]

3. Common Infrastructure

3.1. Scrolling

When a user agent is to perform a scroll#perform-a-scrollReferenced in:3.1. Scrolling4. Extensions to the Window Interface6.1. Element Scrolling Members (2) of a scrolling box box, to a given position position, an associated element element and optionally a scroll behavior behavior (which is "auto" if omitted), the following steps must be run:

  1. Abort any ongoing smooth scroll for box.
  2. If the user agent honors the scroll-behavior property and one of the following are true:
    • behavior is "auto" and element is not null and its computed value of the scroll-behavior property is smooth
    • behavior is smooth
    ...then perform a smooth scroll of box to position. Otherwise, perform an instant scroll of box to position.

When a user agent is to perform a smooth scroll#concept-smooth-scrollReferenced in:3.1. Scrolling (2) (3)4. Extensions to the Window Interface6.1. Element Scrolling Members (2) of a scrolling box box to position, it must update the scroll position of box in a user-agent-defined fashion over a user-agent-defined amount of time. When the scroll is completed, the scroll position of box must be position. The scroll can also be aborted#smooth-scroll-abortedReferenced in:3.1. Scrolling, either by an algorithm or by the user.

When a user agent is to perform an instant scroll#concept-instant-scrollReferenced in:3.1. Scrolling of a scrolling box box to position, it must update the scroll position of box to position.

To scroll to the beginning of the document for a document document, follow these steps:

  1. Let viewport be the viewport that is associated with document.
  2. Let position be the the scroll position viewport would have by aligning the beginning edges of the scrolling area with the beginning edges of viewport.
  3. If position is the same as viewport’s current scroll position, and viewport does not have an ongoing smooth scroll, abort these steps.
  4. Perform a scroll of viewport to position, and document’s root element as the associated element, if there is one, or null otherwise.

Note: This algorithm is used when navigating to the #top fragment identifier, as defined in HTML. [HTML]

3.2. WebIDL values

When asked to normalize non-finite values#normalize-non-finite-valuesReferenced in:4. Extensions to the Window Interface (2)6. Extensions to the Element Interface (2) (3) (4) (5) (6) for a value x, if x is one of the three special floating point literal values (Infinity, -Infinity or NaN), then x must be changed to the value 0. [WEBIDL]

4. Extensions to the Window Interface

enum ScrollBehavior#enumdef-scrollbehaviorReferenced in:4. Extensions to the Window Interface { "auto", "instant", "smooth" };

dictionary ScrollOptions#dictdef-scrolloptionsReferenced in:4. Extensions to the Window Interface6. Extensions to the Element Interface {
    ScrollBehavior behavior#dom-scrolloptions-behaviorReferenced in:4. Extensions to the Window Interface6. Extensions to the Element Interface6.1. Element Scrolling Members = "auto";
};
dictionary ScrollToOptions#dictdef-scrolltooptionsReferenced in:4. Extensions to the Window Interface (2) (3) (4) (5)6. Extensions to the Element Interface (2) (3) (4) (5) : ScrollOptions {
    unrestricted double left#dom-scrolltooptions-leftReferenced in:4. Extensions to the Window Interface (2) (3) (4)6. Extensions to the Element Interface (2) (3) (4) (5) (6);
    unrestricted double top#dom-scrolltooptions-topReferenced in:4. Extensions to the Window Interface (2) (3) (4)6. Extensions to the Element Interface (2) (3) (4) (5) (6);
};

partial interface Window {
    [NewObject] MediaQueryList matchMedia(DOMString query);
    [SameObject, Replaceable] readonly attribute Screen screen;

    // browsing context
    void moveTo(long x, long y);
    void moveBy(long x, long y);
    void resizeTo(long x, long y);
    void resizeBy(long x, long y);

    // viewport
    [Replaceable] readonly attribute long innerWidth;
    [Replaceable] readonly attribute long innerHeight;

    // viewport scrolling
    [Replaceable] readonly attribute double scrollX;
    [Replaceable] readonly attribute double pageXOffset;
    [Replaceable] readonly attribute double scrollY;
    [Replaceable] readonly attribute double pageYOffset;
    void scroll(optional ScrollToOptions options);
    void scroll(unrestricted double x, unrestricted double y);
    void scrollTo(optional ScrollToOptions options);
    void scrollTo(unrestricted double x, unrestricted double y);
    void scrollBy(optional ScrollToOptions options);
    void scrollBy(unrestricted double x, unrestricted double y);

    // client
    [Replaceable] readonly attribute long screenX;
    [Replaceable] readonly attribute long screenY;
    [Replaceable] readonly attribute long outerWidth;
    [Replaceable] readonly attribute long outerHeight;
    [Replaceable] readonly attribute double devicePixelRatio;
};

When the matchMedia(query)#dom-window-matchmediaReferenced in:2.1. CSS pixels4. Extensions to the Window Interface method is invoked these steps must be run:

  1. Let parsed media query list be the result of parsing query.
  2. Return a new MediaQueryList object, with the context object’s associated Document as the document, with parsed media query list as its associated media query list.

The screen#dom-window-screenReferenced in:4. Extensions to the Window Interface (2) attribute must return the Screen object associated with the Window object.

Note: Accessing screen through a WindowProxy object might yield different results when the Document is navigated.

The moveTo(x, y)#dom-window-movetoReferenced in:4. Extensions to the Window InterfaceChanges From 4 August 2011 To 17 December 2013 method must follow these steps:

  1. Optionally, terminate these steps.

  2. Let target be the browsing context of the context object.

  3. Let source be the responsible browsing context of the incumbent settings object.

  4. If source is not allowed to resize and move target, terminate these steps.

  5. Optionally, clamp x and y in a user-agent-defined manner so that the window does not move outside the available space.

  6. Move target’s window such that the window’s top left corner is at coordinates (x, y) relative to the top left corner of the output device, measured in CSS pixels of target. The positive axes are rightward and downward.

The moveBy(x, y)#dom-window-movebyReferenced in:4. Extensions to the Window InterfaceChanges From 4 August 2011 To 17 December 2013 method must follow these steps:

  1. Optionally, terminate these steps.

  2. Let target be the browsing context of the context object.

  3. Let source be the responsible browsing context of the incumbent settings object.

  4. If source is not allowed to resize and move target, terminate these steps.

  5. Optionally, clamp x and y in a user-agent-defined manner so that the window does not move outside the available space.

  6. Move target’s window x CSS pixels of target rightward and y CSS pixels of target downward.

The resizeTo(x, y)#dom-window-resizetoReferenced in:4. Extensions to the Window InterfaceChanges From 4 August 2011 To 17 December 2013 method must follow these steps:

  1. Optionally, terminate these steps.

  2. Let target be the browsing context of the context object.

  3. Let source be the responsible browsing context of the incumbent settings object.

  4. If source is not allowed to resize and move target, terminate these steps.

  5. Optionally, clamp x and y in a user-agent-defined manner so that the window does not get too small or bigger than the available space.

  6. Resize target’s window by moving its right and bottom edges such that the distance between the left and right edges of the viewport are x CSS pixels of target and the distance between the top and bottom edges of the viewport are y CSS pixels of target.

  7. Optionally, move target’s window in a user-agent-defined manner so that it does not grow outside the available space.

The resizeBy(x, y)#dom-window-resizebyReferenced in:4. Extensions to the Window InterfaceChanges From 4 August 2011 To 17 December 2013 method must follow these steps:

  1. Optionally, terminate these steps.

  2. Let target be the browsing context of the context object.

  3. Let source be the responsible browsing context of the incumbent settings object.

  4. If source is not allowed to resize and move target, terminate these steps.

  5. Optionally, clamp x and y in a user-agent-defined manner so that the window does not get too small or bigger than the available space.

  6. Resize target’s window by moving its right edge x CSS pixels of target rightward and its bottom edge y CSS pixels of target downward.

  7. Optionally, move target’s window in a user-agent-defined manner so that it does not grow outside the available space.

A browsing context A is allowed to resize and move#allowed-to-resize-and-moveReferenced in:4. Extensions to the Window Interface (2) (3) (4) a browsing context B if all the following conditions are met:

The innerWidth#dom-window-innerwidthReferenced in:4. Extensions to the Window InterfaceChanges From 4 August 2011 To 17 December 2013 attribute must return the viewport width including the size of a rendered scroll bar (if any), or zero if there is no viewport.

The following snippet shows how to obtain the width of the viewport:
var viewportWidth = innerWidth

The innerHeight#dom-window-innerheightReferenced in:4. Extensions to the Window Interface attribute must return the viewport height including the size of a rendered scroll bar (if any), or zero if there is no viewport.

The scrollX#dom-window-scrollxReferenced in:4. Extensions to the Window Interface (2) (3)6. Extensions to the Element Interface (2) (3) (4) (5)10. Extensions to the MouseEvent Interface attribute attribute must return the x-coordinate, relative to the initial containing block origin, of the left of the viewport, or zero if there is no viewport.

The pageXOffset#dom-window-pagexoffsetReferenced in:4. Extensions to the Window Interface attribute must return the value returned by the scrollX attribute.

The scrollY#dom-window-scrollyReferenced in:4. Extensions to the Window Interface (2) (3)6. Extensions to the Element Interface (2) (3) (4)10. Extensions to the MouseEvent Interface attribute attribute must return the y-coordinate, relative to the initial containing block origin, of the top of the viewport, or zero if there is no viewport.

The pageYOffset#dom-window-pageyoffsetReferenced in:4. Extensions to the Window Interface attribute must return the value returned by the scrollY attribute.

When the scroll()#dom-window-scrollReferenced in:4. Extensions to the Window Interface (2) (3) (4)6. Extensions to the Element Interface (2) (3) (4) (5) (6)Changes From 17 December 2013 method is invoked these steps must be run:

  1. If invoked with one argument, follow these substeps:

    1. Let options be the argument.

    2. Let x be the value of the left dictionary member of options, if present, or the viewport’s current scroll position on the x axis otherwise.

    3. Let y be the value of the top dictionary member of options, if present, or the viewport’s current scroll position on the y axis otherwise.

  2. If invoked with two arguments, follow these substeps:

    1. Let options be null converted to a ScrollToOptions dictionary. [WEBIDL]

    2. Let x and y be the arguments, respectively.

  3. Normalize non-finite values for x and y.

  4. If there is no viewport, abort these steps.

  5. Let viewport width be the width of the viewport excluding the width of the scroll bar, if any.

  6. Let viewport height be the height of the viewport excluding the height of the scroll bar, if any.

  7. If the viewport has rightward overflow direction
    Let x be max(0, min(x, viewport scrolling area width - viewport width)).
    If the viewport has leftward overflow direction
    Let x be min(0, max(x, viewport width - viewport scrolling area width)).
  8. If the viewport has downward overflow direction
    Let y be max(0, min(y, viewport scrolling area height - viewport height)).
    If the viewport has upward overflow direction
    Let y be min(0, max(y, viewport height - viewport scrolling area height)).
  9. Let position be the scroll position the viewport would have by aligning the x-coordinate x of the viewport scrolling area with the left of the viewport and aligning the y-coordinate y of the viewport scrolling area with the top of the viewport.

  10. If position is the same as the viewport’s current scroll position, and the viewport does not have an ongoing smooth scroll, abort these steps.

  11. Let document be the viewport’s associated Document.

  12. Perform a scroll of the viewport to position, document’s root element as the associated element, if there is one, or null otherwise, and the scroll behavior being the value of the behavior dictionary member of options.

When the scrollTo()#dom-window-scrolltoReferenced in:4. Extensions to the Window Interface (2)Changes From 17 December 2013 method is invoked, the user agent must act as if the scroll() method was invoked with the same arguments.

When the scrollBy()#dom-window-scrollbyReferenced in:4. Extensions to the Window Interface (2)Changes From 17 December 2013 method is invoked, the user agent must run these steps:

  1. If invoked with two arguments, follow these substeps:

    1. Let options be null converted to a ScrollToOptions dictionary. [WEBIDL]

    2. Let x and y be the arguments, respectively.

    3. Let the left dictionary member of options have the value x.

    4. Let the top dictionary member of options have the value y.

  2. Normalize non-finite values for the left and top dictionary members of options.

  3. Add the value of scrollX to the left dictionary member.

  4. Add the value of scrollY to the top dictionary member.

  5. Act as if the scroll() method was invoked with options as the only argument.

The screenX#dom-window-screenxReferenced in:4. Extensions to the Window Interface attribute must return the x-coordinate, relative to the origin of the screen of the output device, of the left of the client window as number of pixels, or zero if there is no such thing.

The screenY#dom-window-screenyReferenced in:4. Extensions to the Window Interface attribute must return the y-coordinate, relative to the origin of the screen of the output device, of the top of the client window as number of pixels, or zero if there is no such thing.

The outerWidth#dom-window-outerwidthReferenced in:4. Extensions to the Window Interface attribute must return the width of the client window. If there is no client window this attribute must return zero.

The outerHeight#dom-window-outerheightReferenced in:4. Extensions to the Window Interface attribute must return the height of the client window. If there is no client window this attribute must return zero.

The devicePixelRatio#dom-window-devicepixelratioReferenced in:4. Extensions to the Window InterfaceChanges From 4 August 2011 To 17 December 2013 attribute must return the result of the following algorithm:

  1. If there is no output device, return 1 and abort these steps.

  2. Let CSS pixel size be the size of a CSS pixel at the current page zoom scale factor and at a pinch zoom scale factor of 1.0.

  3. Let device pixel size be the vertical size of a device pixel of the output device.

  4. Return the result of dividing CSS pixel size by device pixel size.

4.1. The features argument to the open() method

HTML defines the open() method but has no defined effect for the third argument, features. [HTML]

This specification defines the effect of the features argument for user agents that do not opt to ignore it, as follows:

  1. If the method does not result in a new auxiliary browsing context being created, terminate these steps.

  2. Let target be the new auxiliary browsing context.

  3. Let tokens be the result of splitting features on commas.

  4. Let parsed features be a new empty dictionary.

  5. Token loop: For each token token in tokens, follow these substeps:

    1. Let input be token.

    2. Let position point at the first character of input.

    3. Skip whitespace.

    4. Collect a sequence of characters that are not space characters nor "=" (U+003D). Let name be the collected characters, converted to ASCII lowercase.

    5. If name is in parsed features or if name is not a supported open() feature name, continue token loop.

    6. Skip whitespace.

    7. If the character at position is not "=" (U+003D), continue token loop.

    8. Advance position by one.

    9. If position is past the end of input, continue token loop.

    10. Collect a sequence of characters that are any characters. Let raw value be the collected characters.

    11. Let value be the result of invoking the rules for parsing integers on raw value.

    12. If value is an error, continue token loop.

    13. Set name in parsed features to value.

  6. If left is present in parsed features, follow these substeps:

    1. Let x be the value of left.

    2. Optionally, clamp x in a user-agent-defined manner so that the window does not move outside the available space.

    3. Optionally, move target’s window such that the window’s left edge is at the horizontal coordinate x relative to the left edge of the output device, measured in CSS pixels of target. The positive axis is rightward.

  7. If top is present in parsed features, follow these substeps:

    1. Let y be the value of top.

    2. Optionally, clamp y in a user-agent-defined manner so that the window does not move outside the available space.

    3. Optionally, move target’s window such that the window’s top edge is at the vertical coordinate y relative to the top edge of the output device, measured in CSS pixels of target. The positive axis is downward.

  8. If width is present in parsed features, follow these substeps:

    1. Let x be the value of width.

    2. Optionally, clamp x in a user-agent-defined manner so that the window does not get too small or bigger than the available space.

    3. Optionally, size target’s window by moving its right edge such that the distance between the left and right edges of the viewport are x CSS pixels of target.

    4. Optionally, move target’s window in a user-agent-defined manner so that it does not grow outside the available space.

  9. If height is present in parsed features, follow these substeps:

    1. Let y be the value of height.

    2. Optionally, clamp y in a user-agent-defined manner so that the window does not get too small or bigger than the available space.

    3. Optionally, size target’s window by moving its bottom edge such that the distance between the top and bottom edges of the viewport are y CSS pixels of target.

    4. Optionally, move target’s window in a user-agent-defined manner so that it does not grow outside the available space.

A supported open() feature name#supported-open-feature-nameReferenced in:4.1. The features argument to the open() method is one of the following:

width#supported-open-feature-name-widthReferenced in:4.1. The features argument to the open() method (2)
The width of the viewport.
height#supported-open-feature-name-heightReferenced in:4.1. The features argument to the open() method (2)
The height of the viewport.
left#supported-open-feature-name-leftReferenced in:4.1. The features argument to the open() method (2)
The left position of the window.
top#supported-open-feature-name-topReferenced in:4.1. The features argument to the open() method (2)
The top position of the window.

4.2. The MediaQueryList Interface

This section integrates with the event loop defined in HTML. [HTML]

A MediaQueryList object has an associated media query list#media-query-listReferenced in:4. Extensions to the Window Interface4.2. The MediaQueryList Interface (2) and an associated document#mediaquerylist-documentReferenced in:4. Extensions to the Window Interface4.2. The MediaQueryList Interface (2) set on creation.

A MediaQueryList object has an associated media#mediaquerylist-mediaReferenced in:4.2. The MediaQueryList Interface (2) which is the serialized form of the associated media query list.

A MediaQueryList object has an associated matches state#mediaquerylist-matches-stateReferenced in:4.2. The MediaQueryList Interface (2) (3)4.2.1. Event summary which is true if the associated media query list matches the state of the document, and false otherwise.

When asked to evaluate media queries and report changes for a Document doc, run these steps:

  1. For each MediaQueryList object target that has doc as its document, in the order they were created, oldest first, run these substeps:

    1. If target’s matches state has changed since the last time these steps were run, dispatch a new event to target using the MediaQueryList interface, with its type attribute initialized to change, its isTrusted attribute initialized to true, its media attribute initialized to target’s media, and its matches attribute initialized to target’s matches state.
A simple piece of code that detects changes in the orientation of the viewport can be written as follows:
function handleOrientationChange(event) {
    if(event.matches) // landscape
        
    else
        
}
var mql = matchMedia("(orientation:landscape)");
mql.onchange = handleOrientationChange;
interface MediaQueryList#mediaquerylistReferenced in:4. Extensions to the Window Interface (2)4.2. The MediaQueryList Interface (2) (3) (4) (5) (6) (7) (8)4.2.1. Event summary (2)Changes From 17 December 2013 (2) : EventTarget {
  readonly attribute DOMString media;
  readonly attribute boolean matches;
  void addListener(EventListener? listener);
  void removeListener(EventListener? listener);
           attribute EventHandler onchange;
};

The media#dom-mediaquerylist-mediaReferenced in:4.2. The MediaQueryList Interface (2) attribute must return the associated media.

The matches#dom-mediaquerylist-matchesReferenced in:4.2. The MediaQueryList Interface attribute must return the associated matches state.

The addListener(listener)#dom-mediaquerylist-addlistenerReferenced in:4.2. The MediaQueryList Interface (2) (3)Changes From 17 December 2013 method must run these steps:

  1. If listener is null, terminate these steps.

  2. Append an event listener to the associated list of event listeners with type set to change, callback set to listener, and capture set to false, unless there already is an event listener in that list with the same type, callback, and capture.

The removeListener(listener)#dom-mediaquerylist-removelistenerReferenced in:4.2. The MediaQueryList Interface (2) (3) method must run these steps:

  1. Remove an event listener from the associated list of event listeners, whose type is change, callback is listener, and capture is false.

Note: This specification initially had a custom callback mechanism with addListener() and removeListener(), and the callback was invoked with the associated media query list as argument. Now the normal event mechanism is used instead. For backwards compatibility, the addListener() and removeListener() methods are basically aliases for addEventListener() and removeEventListener(), respectively, and the change event masquerades as a MediaQueryList.

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 MediaQueryList interface:

Event handler Event handler event type
onchange#dom-mediaquerylist-onchangeReferenced in:4.2. The MediaQueryList Interface change
[Constructor(DOMString type, optional MediaQueryListEventInit eventInitDict)]
interface MediaQueryListEvent : Event {
  readonly attribute DOMString media;
  readonly attribute boolean matches;
};

dictionary MediaQueryListEventInit#dictdef-mediaquerylisteventinitReferenced in:4.2. The MediaQueryList Interface : EventInit {
  DOMString media = "";
  boolean matches = false;
};

The media#dom-mediaquerylistevent-mediaReferenced in:4.2. The MediaQueryList Interface attribute must return the value it was initialized to.

The matches#dom-mediaquerylistevent-matchesReferenced in:4.2. The MediaQueryList Interface (2) attribute must return the value it was initialized to.

4.2.1. Event summary

This section is non-normative.

Event Interface Interesting targets Description
change#eventdef-mediaquerylist-changeReferenced in:4.2. The MediaQueryList Interface (2) Event MediaQueryList Fired at the MediaQueryList when the matches state changes.

4.3. The Screen Interface

As its name suggests, the Screen interface represents information about the screen of the output device.

interface Screen#screenReferenced in:4. Extensions to the Window Interface (2)4.3. The Screen Interface (2)Changes From 4 August 2011 To 17 December 2013 {
  readonly attribute long availWidth;
  readonly attribute long availHeight;
  readonly attribute long width;
  readonly attribute long height;
  readonly attribute unsigned long colorDepth;
  readonly attribute unsigned long pixelDepth;
};

The availWidth#dom-screen-availwidthReferenced in:4.3. The Screen Interface attribute must return the available width of the rendering surface of the output device, in CSS pixels.

The availHeight#dom-screen-availheightReferenced in:4.3. The Screen Interface attribute must return the available height of the rendering surface of the output device, in CSS pixels.

The width#dom-screen-widthReferenced in:4.3. The Screen Interface attribute must return the width of the output device, in CSS pixels.

The height#dom-screen-heightReferenced in:4.3. The Screen Interface attribute must return the height of the output device, in CSS pixels.

The colorDepth#dom-screen-colordepthReferenced in:4.3. The Screen Interface (2)Changes From 4 August 2011 To 17 December 2013 attribute must return 24.

The pixelDepth#dom-screen-pixeldepthReferenced in:4.3. The Screen Interface (2)Changes From 4 August 2011 To 17 December 2013 attribute must return 24.

Note: The colorDepth and pixelDepth attributes are useless but are included for compatibility.

5. Extensions to the Document Interface

partial interface Document {
  Element? elementFromPoint(double x, double y);
  sequence<Element> elementsFromPoint(double x, double y);
  CaretPosition? caretPositionFromPoint(double x, double y);
  readonly attribute Element? scrollingElement;
};

The elementFromPoint(x, y)#dom-document-elementfrompointReferenced in:5. Extensions to the Document Interface (2) (3) method must follow these steps:

  1. If either argument is negative, x is greater than the viewport width excluding the size of a rendered scroll bar (if any), or y is greater than the viewport height excluding the size of a rendered scroll bar (if any), or there is no viewport associated with the document, return null and terminate these steps.

  2. If there is a layout box in the viewport that would be a target for hit testing at coordinates x,y, when applying the transforms that apply to the descendants of the viewport, return the associated element and terminate these steps.

  3. If the document has a root element, return the root element and terminate these steps.

  4. Return null.

Note: The elementFromPoint() method does not necessarily return the top-most painted element. For instance, an element can be excluded from being a target for hit testing by using the pointer-events CSS property.

The elementsFromPoint(x, y)#dom-document-elementsfrompointReferenced in:5. Extensions to the Document InterfaceChanges From 4 August 2011 To 17 December 2013 method must follow these steps:

  1. Let sequence be a new empty sequence.

  2. If either argument is negative, x is greater than the viewport width excluding the size of a rendered scroll bar (if any), or y is greater than the viewport height excluding the size of a rendered scroll bar (if any), or there is no viewport associated with the document, return sequence and terminate these steps.

  3. For each layout box in the viewport, in paint order, starting with the topmost box, that would be a target for hit testing at coordinates x,y even if nothing would be overlapping it, when applying the transforms that apply to the descendants of the viewport, append the associated element to sequence.

  4. If the document has a root element, and the last item in sequence is not the root element, append the root element to sequence.

  5. Return sequence.

The caretPositionFromPoint(x, y)#dom-document-caretpositionfrompointReferenced in:5. Extensions to the Document Interface (2) method must return the result of running these steps:

  1. If there is no viewport associated with the document, return null.

  2. If either argument is negative, x is greater than the viewport width excluding the size of a rendered scroll bar (if any), y is greater than the viewport height excluding the size of a rendered scroll bar (if any) return null.

  3. If at the coordinates x,y in the viewport no text insertion point indicator would have been inserted when applying the transforms that apply to the descendants of the viewport, return null.

  4. If at the coordinates x,y in the viewport a text insertion point indicator would have been inserted in a text entry widget which is also a replaced element, when applying the transforms that apply to the descendants of the viewport, return a caret position with its properties set as follows:

    caret node
    The node corresponding to the text entry widget.
    caret offset
    The amount of 16-bit units to the left of where the text insertion point indicator would have inserted.
    caret range
    null
  5. Otherwise, return a caret position where the caret range is a collapsed Range object for the position where the text insertion point indicator would have been inserted when applying the transforms that apply to the descendants of the viewport, and the other properties are set as follows:

    caret node
    The startContainer of the caret range.
    caret offset
    The startOffset of the caret range.

Note: The specifics of hit testing are out of scope of this specification and therefore the exact details of elementFromPoint() and caretPositionFromPoint() are therefore too. Hit testing will hopefully be defined in a future revision of CSS or HTML.

The scrollingElement#dom-document-scrollingelementReferenced in:5. Extensions to the Document Interface (2)Changes From 17 December 2013 attribute, on getting, must run these steps:

  1. If the Document is in quirks mode, follow these substeps:

    1. If the HTML body element exists, and it is not potentially scrollable, return the HTML body element and abort these steps.

    2. Return null and abort these steps.

  2. If there is a root element, return the root element and abort these steps.

  3. Return null.

Note: For non-conforming user agents that always use the quirks mode behavior for scrollTop and scrollLeft, the scrollingElement attribute is expected to also always return the HTML body element (or null if it does not exist). This API exists so that Web developers can use it to get the right element to use for scrolling APIs, without making assumptions about a particular user agent’s behavior or having to invoke a scroll to see which element scrolls the viewport.

Note: The HTML body element is different from HTML’s document.body in that the latter can return a frameset element.

5.1. The CaretPosition Interface

A caret position#caret-positionReferenced in:5. Extensions to the Document Interface (2) gives the position of a text insertion point indicator. It always has an associated caret node#caret-nodeReferenced in:5. Extensions to the Document Interface (2)5.1. The CaretPosition Interface (2), caret offset#caret-offsetReferenced in:5. Extensions to the Document Interface (2)5.1. The CaretPosition Interface (2), and caret range#caret-rangeReferenced in:5. Extensions to the Document Interface (2) (3) (4)5.1. The CaretPosition Interface. It is represented by a CaretPosition object.

interface CaretPosition#caretpositionReferenced in:5. Extensions to the Document Interface5.1. The CaretPosition Interface (2) {
  readonly attribute Node offsetNode;
  readonly attribute unsigned long offset;
  [NewObject] DOMRect? getClientRect();
};

The offsetNode#dom-caretposition-offsetnodeReferenced in:5.1. The CaretPosition Interface attribute must return the caret node.

The offset#dom-caretposition-offsetReferenced in:5.1. The CaretPosition Interface attribute must return the caret offset.

The getClientRect()#dom-caretposition-getclientrectReferenced in:5.1. The CaretPosition Interface method must follow these steps, aborting on the first step that returns a value:

  1. If caret range is not null:

    1. Let list be the result of invoking the getClientRects() method on the range.

    2. If list is empty, return null.

    3. Return the DOMRect object in list at index 0.

  2. If caret node is a text entry widget that is a replaced element, and that is in the document, return a static DOMRect object for the caret in the widget as represented by the caret offset value. The transforms that apply to the element and its ancestors are applied.

  3. Return null.

6. Extensions to the Element Interface

enum ScrollLogicalPosition#enumdef-scrolllogicalpositionReferenced in:6. Extensions to the Element Interface (2) { "start", "center", "end", "nearest" };
dictionary ScrollIntoViewOptions#dictdef-scrollintoviewoptionsReferenced in:6. Extensions to the Element Interface6.1. Element Scrolling Members : ScrollOptions {
  ScrollLogicalPosition block#dom-scrollintoviewoptions-blockReferenced in:6. Extensions to the Element Interface (2)6.1. Element Scrolling Members (2) (3) = "center";
  ScrollLogicalPosition inline#dom-scrollintoviewoptions-inlineReferenced in:6. Extensions to the Element Interface (2)6.1. Element Scrolling Members (2) (3) = "center";
};

partial interface Element {
  sequence<DOMRect> getClientRects();
  [NewObject] DOMRect getBoundingClientRect();
  void scrollIntoView();
  void scrollIntoView((boolean or object) arg);
  void scroll(optional ScrollToOptions options);
  void scroll(unrestricted double x, unrestricted double y);
  void scrollTo(optional ScrollToOptions options);
  void scrollTo(unrestricted double x, unrestricted double y);
  void scrollBy(optional ScrollToOptions options);
  void scrollBy(unrestricted double x, unrestricted double y);
  attribute unrestricted double scrollTop;
  attribute unrestricted double scrollLeft;
  readonly attribute long scrollWidth;
  readonly attribute long scrollHeight;
  readonly attribute long clientTop;
  readonly attribute long clientLeft;
  readonly attribute long clientWidth;
  readonly attribute long clientHeight;
};

The getClientRects()#dom-element-getclientrectsReferenced in:6. Extensions to the Element Interface (2)9. Extensions to the Range Interface method, when invoked, must return the result of the following algorithm:

  1. If the element on which it was invoked does not have an associated layout box return an empty sequence and stop this algorithm.

  2. If the element has an associated SVG layout box return a sequence containing a single DOMRect object that describes the bounding box of the element as defined by the SVG specification, applying the transforms that apply to the element and its ancestors.

  3. Return a sequence containing static DOMRect objects in content order, one for each box fragment, describing its border area (including those with a height or width of zero) with the following constraints:

    • Apply the transforms that apply to the element and its ancestors.

    • If the element on which the method was invoked has a computed value for the display property of table or inline-table include both the table box and the caption box, if any, but not the anonymous container box.

    • Replace each anonymous block box with its child box(es) and repeat this until no anonymous block boxes are left in the final list.

The getBoundingClientRect()#dom-element-getboundingclientrectReferenced in:6. Extensions to the Element Interface6.1. Element Scrolling Members method, when invoked, must return the result of the following algorithm:

  1. Let list be the result of invoking getClientRects() on the same element this method was invoked on.

  2. If the list is empty return a static DOMRect object whose x, y, width and height members are zero.

  3. Otherwise, return a static DOMRect object describing the smallest rectangle that includes the first rectangle in list and all of the remaining rectangles of which the height or width is not zero.

The following snippet gets the dimensions of the first div element in a document:
var example = document.getElementsByTagName("div")[0].getBoundingClientRect();
var exampleWidth = example.width;
var exampleHeight = example.height;

The scrollIntoView(arg)#dom-element-scrollintoviewReferenced in:6. Extensions to the Element Interface (2)Changes From 17 December 2013 (2) method must run these steps:

  1. Let options be null.

  2. If arg is an object, let options be arg.

  3. Convert options to a ScrollIntoViewOptions dictionary. [WEBIDL]

  4. If arg is not specified or is true, let the block dictionary member of options have the value "start", and let the inline dictionary member of options have the value "nearest".

  5. If arg is false, let the block dictionary member of options have the value "end", and let the inline dictionary member of options have the value "nearest".

  6. If the element does not have any associated layout box terminate these steps.

  7. Scroll the element into view with the options options.

  8. Optionally perform some other action that brings the element to the user’s attention.

The scroll()#dom-element-scrollReferenced in:6. Extensions to the Element Interface (2) (3) (4)Changes From 17 December 2013 method must run these steps:

  1. If invoked with one argument, follow these substeps:

    1. Let options be the argument.

    2. Normalize non-finite values for left and top dictionary members of options, if present.

    3. Let x be the value of the left dictionary member of options, if present, or the element’s current scroll position on the x axis otherwise.

    4. Let y be the value of the top dictionary member of options, if present, or the element’s current scroll position on the y axis otherwise.

  2. If invoked with two arguments, follow these substeps:

    1. Let options be null converted to a ScrollToOptions dictionary. [WEBIDL]

    2. Let x and y be the arguments, respectively.

    3. Normalize non-finite values for x and y.

    4. Let the left dictionary member of options have the value x.

    5. Let the top dictionary member of options have the value y.

  3. Let document be the element’s node document.

  4. If document is not the active document, terminate these steps.

  5. Let window be the value of document’s defaultView attribute.

  6. If window is null, terminate these steps.

  7. If the element is the root element and document is in quirks mode, terminate these steps.

  8. If the element is the root element invoke scroll() on window with scrollX on window as first argument and y as second argument, and terminate these steps.

  9. If the element is the HTML body element, document is in quirks mode, and the element is not potentially scrollable, invoke scroll() on window with options as the only argument, and terminate these steps.

  10. If the element does not have any associated CSS layout box, the element has no associated scrolling box, or the element has no overflow, terminate these steps.

  11. Scroll the element to x,y, with the scroll behavior being the value of the behavior dictionary member of options.

When the scrollTo()#dom-element-scrolltoReferenced in:6. Extensions to the Element Interface (2)Changes From 17 December 2013 method is invoked, the user agent must act as if the scroll() method was invoked with the same arguments.

When the scrollBy()#dom-element-scrollbyReferenced in:6. Extensions to the Element Interface (2)Changes From 17 December 2013 method is invoked, the user agent must run these steps:

  1. If invoked with one argument, follow these substeps:

    1. Let options be the argument.

    2. Normalize non-finite values for left and top dictionary members of options, if present.

  2. If invoked with two arguments, follow these substeps:

    1. Let options be null converted to a ScrollToOptions dictionary. [WEBIDL]

    2. Let x and y be the arguments, respectively.

    3. Normalize non-finite values for x and y.

    4. Let the left dictionary member of options have the value x.

    5. Let the top dictionary member of options have the value y.

  3. Add the value of scrollLeft to the left dictionary member.

  4. Add the value of scrollTop to the top dictionary member.

  5. Act as if the scroll() method was invoked with options as the only argument.

The scrollTop#dom-element-scrolltopReferenced in:5. Extensions to the Document Interface6. Extensions to the Element Interface (2) (3) (4)Changes From 17 December 2013 attribute, on getting, must return the result of running these steps:

  1. Let document be the element’s node document.

  2. If document is not the active document, return zero and terminate these steps.

  3. Let window be the value of document’s defaultView attribute.

  4. If window is null, return zero and terminate these steps.

  5. If the element is the root element and document is in quirks mode, return zero and terminate these steps.

  6. If the element is the root element return the value of scrollY on window.

  7. If the element is the HTML body element, document is in quirks mode, and the element is not potentially scrollable, return the value of scrollY on window.

  8. If the element does not have any associated CSS layout box, return zero and terminate these steps.

  9. Return the y-coordinate of the scrolling area at the alignment point with the top of the padding edge of the element.

When setting the scrollTop attribute these steps must be run:

  1. Let y be the given value.

  2. Normalize non-finite values for y.

  3. Let document be the element’s node document.

  4. If document is not the active document, terminate these steps.

  5. Let window be the value of document’s defaultView attribute.

  6. If window is null, terminate these steps.

  7. If the element is the root element and document is in quirks mode, terminate these steps.

  8. If the element is the root element invoke scroll() on window with scrollX on window as first argument and y as second argument, and terminate these steps.

  9. If the element is the HTML body element, document is in quirks mode, and the element is not potentially scrollable, invoke scroll() on window with scrollX as first argument and y as second argument, and terminate these steps.

  10. If the element does not have any associated CSS layout box, the element has no associated scrolling box, or the element has no overflow, terminate these steps.

  11. Scroll the element to scrollLeft,y, with the scroll behavior being "auto".

The scrollLeft#dom-element-scrollleftReferenced in:5. Extensions to the Document Interface6. Extensions to the Element Interface (2) (3) (4)Changes From 17 December 2013 (2) attribute, on getting, must return the result of running these steps:

  1. Let document be the element’s node document.

  2. If document is not the active document, return zero and terminate these steps.

  3. Let window be the value of document’s defaultView attribute.

  4. If window is null, return zero and terminate these steps.

  5. If the element is the root element and document is in quirks mode, return zero and terminate these steps.

  6. If the element is the root element return the value of scrollX on window.

  7. If the element is the HTML body element, document is in quirks mode, and the element is not potentially scrollable, return the value of scrollX on window.

  8. If the element does not have any associated CSS layout box, return zero and terminate these steps.

  9. Return the x-coordinate of the scrolling area at the alignment point with the left of the padding edge of the element.

When setting the scrollLeft attribute these steps must be run:

  1. Let x be the given value.

  2. Normalize non-finite values for x.

  3. Let document be the element’s node document.

  4. If document is not the active document, terminate these steps.

  5. Let window be the value of document’s defaultView attribute.

  6. If window is null, terminate these steps.

  7. If the element is the root element and document is in quirks mode, terminate these steps.

  8. If the element is the root element invoke scroll() on window with x as first argument and scrollY on window as second argument, and terminate these steps.

  9. If the element is the HTML body element, document is in quirks mode, and the element is not potentially scrollable, invoke scroll() on window with x as first argument and scrollY on window as second argument, and terminate these steps.

  10. If the element does not have any associated CSS layout box, the element has no associated scrolling box, or the element has no overflow, terminate these steps.

  11. Scroll the element to x,scrollTop, with the scroll behavior being "auto".

The scrollWidth#dom-element-scrollwidthReferenced in:6. Extensions to the Element InterfaceChanges From 17 December 2013 attribute must return the result of running these steps:

  1. Let document be the element’s node document.

  2. If document is not the active document, return zero and terminate these steps.

  3. Let viewport width be the width of the viewport excluding the width of the scroll bar, if any, or zero if there is no viewport.

  4. If the element is the root element and document is not in quirks mode return max(viewport scrolling area width, viewport width).

  5. If the element is the HTML body element, document is in quirks mode and the element is not potentially scrollable, return max(viewport scrolling area width, viewport width).

  6. If the element does not have any associated CSS layout box return zero and terminate these steps.

  7. Return the width of the element’s scrolling area.

The scrollHeight#dom-element-scrollheightReferenced in:6. Extensions to the Element InterfaceChanges From 17 December 2013 attribute must return the result of running these steps:

  1. Let document be the element’s node document.

  2. If document is not the active document, return zero and terminate these steps.

  3. Let viewport height be the height of the viewport excluding the height of the scroll bar, if any, or zero if there is no viewport.

  4. If the element is the root element and document is not in quirks mode return max(viewport scrolling area height, viewport height).

  5. If the element is the HTML body element, document is in quirks mode and the element is not potentially scrollable, return max(viewport scrolling area height, viewport height).

  6. If the element does not have any associated CSS layout box return zero and terminate these steps.

  7. Return the height of the element’s scrolling area.

The clientTop#dom-element-clienttopReferenced in:6. Extensions to the Element InterfaceChanges From 17 December 2013 attribute must run these steps:

  1. If the element has no associated CSS layout box or if the CSS layout box is inline, return zero.

  2. Return the computed value of the border-top-width property plus the height of any scrollbar rendered between the top padding edge and the top border edge, ignoring any transforms that apply to the element and its ancestors.

The clientLeft#dom-element-clientleftReferenced in:6. Extensions to the Element InterfaceChanges From 17 December 2013 attribute must run these steps:

  1. If the element has no associated CSS layout box or if the CSS layout box is inline, return zero.

  2. Return the computed value of the border-left-width property plus the width of any scrollbar rendered between the left padding edge and the left border edge, ignoring any transforms that apply to the element and its ancestors.

The clientWidth#dom-element-clientwidthReferenced in:6. Extensions to the Element InterfaceChanges From 17 December 2013 attribute must run these steps:

  1. If the element has no associated CSS layout box or if the CSS layout box is inline, return zero.

  2. If the element is the root element and the element’s node document is not in quirks mode, or if the element is the HTML body element and the element’s node document is in quirks mode, return the viewport width excluding the size of a rendered scroll bar (if any).

  3. Return the width of the padding edge excluding the width of any rendered scrollbar between the padding edge and the border edge, ignoring any transforms that apply to the element and its ancestors.

The clientHeight#dom-element-clientheightReferenced in:6. Extensions to the Element InterfaceChanges From 17 December 2013 attribute must run these steps:

  1. If the element has no associated CSS layout box or if the CSS layout box is inline, return zero.

  2. If the element is the root element and the element’s node document is not in quirks mode, or if the element is the HTML body element and the element’s node document is in quirks mode, return the viewport height excluding the size of a rendered scroll bar (if any).

  3. Return the height of the padding edge excluding the height of any rendered scrollbar between the padding edge and the border edge, ignoring any transforms that apply to the element and its ancestors.

6.1. Element Scrolling Members

To scroll an element into view#scroll-an-element-into-viewReferenced in:6. Extensions to the Element Interface element, with a ScrollIntoViewOptions dictionary options, means to run these steps for each ancestor element or viewport that establishes a scrolling box scrolling box, in order of innermost to outermost scrolling box:

  1. If the Document associated with element is not same origin with the Document associated with the element or viewport associated with box, terminate these steps.

  2. Let element bounding border box be the box that the return value of invoking getBoundingClientRect() on element represents.

  3. Let scrolling box edge A be the beginning edge in the block flow direction of scrolling box, and let element edge A be element bounding border box’s edge on the same physical side as that of scrolling box edge A.

  4. Let scrolling box edge B be the ending edge in the block flow direction of scrolling box, and let element edge B be element bounding border box’s edge on the same physical side as that of scrolling box edge B.

  5. Let scrolling box edge C be the beginning edge in the inline base direction of scrolling box, and let element edge C be element bounding border box’s edge on the same physical side as that of scrolling box edge C.

  6. Let scrolling box edge D be the ending edge in the inline base direction of scrolling box, and let element edge D be element bounding border box’s edge on the same physical side as that of scrolling box edge D.

  7. Let element width be the distance between element edge C and element edge D.

  8. Let scrolling box width be the distance between scrolling box edge C and scrolling box edge D.

  9. Let position be the scroll position scrolling box would have by following these steps:

    1. If the block dictionary member of options is "start", align element edge A with scrolling box edge A.

    2. Otherwise, if the block dictionary member of options is "end"; align element edge B with scrolling box edge B.

    3. Otherwise, if the block dictionary member of options is "center"; align the center of element bounding border box with the center of scrolling box in scrolling box’s block flow direction.

    4. Otherwise, it is "nearest"; follow these steps:

      If element edge A and element edge B are both outside scrolling box edge A and scrolling box edge B
      Do nothing.
      If element edge A is outside scrolling box edge A and element width is less than scrolling box width
      If element edge B is outside scrolling box edge B and element width is greater than scrolling box width
      Align element edge A with scrolling box edge A.
      If element edge A is outside scrolling box edge A and element width is greater than scrolling box width
      If element edge B is outside scrolling box edge B and element width is less than scrolling box width
      Align element edge B with scrolling box edge B.
    5. If the inline dictionary member of options is "start", align element edge C with scrolling box edge C.

    6. Otherwise, if the inline dictionary member of options is "end"; align element edge D with scrolling box edge D.

    7. Otherwise, if the inline dictionary member of options is "center", align the center of element bounding border box with the center of scrolling box in scrolling box’s inline base direction.

    8. Otherwise, it is "nearest"; follow these steps:

      If element edge C and element edge D are both outside scrolling box edge C and scrolling box edge D
      Do nothing.
      If element edge C is outside scrolling box edge C and element width is less than scrolling box width
      If element edge D is outside scrolling box edge D and element width is greater than scrolling box width
      Align element edge C with scrolling box edge C.
      If element edge C is outside scrolling box edge C and element width is greater than scrolling box width
      If element edge D is outside scrolling box edge D and element width is less than scrolling box width
      Align element edge D with scrolling box edge D.
  10. If position is the same as scrolling box’s current scroll position, and scrolling box does not have an ongoing smooth scroll, abort these steps.

  11. If scrolling box is associated with an element
    Let associated element be the element.
    If scrolling box is associated with a viewport
    Let document be the viewport’s associated Document. Let associated element be document’s root element, if there is one, or null otherwise.
  12. Let behavior be the behavior dictionary member of options.

  13. Perform a scroll of scrolling box to position, associated element as the associated element and behavior as the scroll behavior.

To scroll an element#scroll-an-elementReferenced in:6. Extensions to the Element Interface (2) (3) element to x,y optionally with a scroll behavior behavior (which is "auto" if omitted) means to:

  1. Let box be element’s associated scrolling box.

  2. If box has rightward overflow direction
    Let x be max(0, min(x, element scrolling area width - element padding edge width)).
    If box has leftward overflow direction
    Let x be min(0, max(x, element padding edge width - element scrolling area width)).
  3. If box has downward overflow direction
    Let y be max(0, min(y, element scrolling area height - element padding edge height)).
    If box has upward overflow direction
    Let y be min(0, max(y, element padding edge height - element scrolling area height)).
  4. Let position be the scroll position box would have by aligning scrolling area x-coordinate x with the left of box and aligning scrolling area y-coordinate y with the top of box.

  5. If position is the same as box’s current scroll position, and box does not have an ongoing smooth scroll, abort these steps.

  6. Perform a scroll of box to position, element as the associated element and behavior as the scroll behavior.

7. Extensions to the HTMLElement Interface

partial interface HTMLElement {
  readonly attribute Element? offsetParent;
  readonly attribute long offsetTop;
  readonly attribute long offsetLeft;
  readonly attribute long offsetWidth;
  readonly attribute long offsetHeight;
};

The offsetParent#dom-htmlelement-offsetparentReferenced in:7. Extensions to the HTMLElement Interface (2) (3) (4) (5) attribute must return the result of running these steps:

  1. If any of the following holds true return null and terminate this algorithm:

  2. Return the nearest ancestor element of the element for which at least one of the following is true and terminate this algorithm if such an ancestor is found:

  3. Return null.

The offsetTop#dom-htmlelement-offsettopReferenced in:7. Extensions to the HTMLElement Interface attribute must return the result of running these steps:

  1. If the element is the HTML body element or does not have any associated CSS layout box return zero and terminate this algorithm.

  2. If the offsetParent of the element is null return the y-coordinate of the top border edge of the first CSS layout box associated with the element, relative to the initial containing block origin, ignoring any transforms that apply to the element and its ancestors, and terminate this algorithm.

  3. Return the result of subtracting the y-coordinate of the top padding edge of the first CSS layout box associated with the offsetParent of the element from the y-coordinate of the top border edge of the first CSS layout box associated with the element, relative to the initial containing block origin, ignoring any transforms that apply to the element and its ancestors.

    Note: An inline element that consists of multiple line boxes will only have its first CSS layout box considered.

The offsetLeft#dom-htmlelement-offsetleftReferenced in:7. Extensions to the HTMLElement Interface attribute must return the result of running these steps:

  1. If the element is the HTML body element or does not have any associated CSS layout box return zero and terminate this algorithm.

  2. If the offsetParent of the element is null return the x-coordinate of the left border edge of the first CSS layout box associated with the element, relative to the initial containing block origin, , ignoring any transforms that apply to the element and its ancestors, and terminate this algorithm.

  3. Return the result of subtracting the x-coordinate of the left padding edge of the first CSS layout box associated with the offsetParent of the element from the x-coordinate of the left border edge of the first CSS layout box associated with the element, relative to the initial containing block origin, ignoring any transforms that apply to the element and its ancestors.

The offsetWidth#dom-htmlelement-offsetwidthReferenced in:7. Extensions to the HTMLElement Interface attribute must return the result of running these steps:

  1. If the element does not have any associated CSS layout box return zero and terminate this algorithm.

  2. Return the border edge width of the first CSS layout box associated with the element, ignoring any transforms that apply to the element and its ancestors.

The offsetHeight#dom-htmlelement-offsetheightReferenced in:7. Extensions to the HTMLElement Interface attribute must return the result of running these steps:

  1. If the element does not have any associated CSS layout box return zero and terminate this algorithm.

  2. Return the border edge height of the first CSS layout box associated with the element, ignoring any transforms that apply to the element and its ancestors.

8. Extensions to the HTMLImageElement Interface

partial interface HTMLImageElement {
  readonly attribute long x;
  readonly attribute long y;
};

The x#dom-htmlimageelement-xReferenced in:8. Extensions to the HTMLImageElement Interface attribute, on getting, must return the x-coordinate of the left border edge of the first CSS layout box associated with the element, relative to the initial containing block origin, ignoring any transforms that apply to the element and its ancestors, or zero if there is no CSS layout box.

The y#dom-htmlimageelement-yReferenced in:8. Extensions to the HTMLImageElement Interface attribute, on getting, must return the y-coordinate of the top border edge of the first CSS layout box associated with the element, relative to the initial containing block origin, ignoring any transforms that apply to the element and its ancestors, or zero if there is no CSS layout box.

9. Extensions to the Range Interface

The objects the methods described below return must be static.

partial interface Range {
  sequence<DOMRect> getClientRects();
  [NewObject] DOMRect getBoundingClientRect();
};

The getClientRects()#dom-range-getclientrectsReferenced in:5.1. The CaretPosition Interface9. Extensions to the Range Interface (2) method, when invoked, must return an empty sequence if the range is not in the document and otherwise a sequence object containing static DOMRect objects in content order that matches the following constraints:

The getBoundingClientRect()#dom-range-getboundingclientrectReferenced in:9. Extensions to the Range Interface method, when invoked, must return the result of the following algorithm:

  1. Let list be the result of invoking getClientRects() on the same range this method was invoked on.

  2. If list is empty return a static DOMRect object whose x, y, width and height members are zero.

  3. Otherwise, return a static DOMRect object describing the smallest rectangle that includes the first rectangle in list and all of the remaining rectangles of which the height or width is not zero.

10. Extensions to the MouseEvent Interface

The object IDL fragment redefines some members. Can we resolve this somehow?

partial interface MouseEvent {
  readonly attribute double screenX;
  readonly attribute double screenY;
  readonly attribute double pageX;
  readonly attribute double pageY;
  readonly attribute double clientX;
  readonly attribute double clientY;
  readonly attribute double x;
  readonly attribute double y;
  readonly attribute double offsetX;
  readonly attribute double offsetY;
};

partial dictionary MouseEventInit {
  double screenX = 0.0;
  double screenY = 0.0;
  double clientX = 0.0;
  double clientY = 0.0;
};

The screenX#dom-mouseevent-screenxReferenced in:10. Extensions to the MouseEvent Interface attribute must return the x-coordinate of the position where the event occurred relative to the origin of the screen.

The screenY#dom-mouseevent-screenyReferenced in:10. Extensions to the MouseEvent Interface attribute must return the y-coordinate of the position where the event occurred relative to the origin of the screen.

The pageX#dom-mouseevent-pagexReferenced in:10. Extensions to the MouseEvent Interface (2) attribute must follow these steps:

  1. If the event’s dispatch flag is set, return the horizontal coordinate of the position where the event occurred relative to the origin of the initial containing block and terminate these steps.

  2. Let offset be the value of the scrollX attribute of the event’s associated Window object, if there is one, or zero otherwise.

  3. Return the sum of offset and the value of the event’s clientX attribute.

The pageY#dom-mouseevent-pageyReferenced in:10. Extensions to the MouseEvent Interface (2) attribute must follow these steps:

  1. If the event’s dispatch flag is set, return the vertical coordinate of the position where the event occurred relative to the origin of the initial containing block and terminate these steps.

  2. Let offset be the value of the scrollY attribute of the event’s associated Window object, if there is one, or zero otherwise.

  3. Return the sum of offset and the value of the event’s clientY attribute.

The clientX#dom-mouseevent-clientxReferenced in:10. Extensions to the MouseEvent Interface (2) (3) attribute must return the x-coordinate of the position where the event occurred relative to the origin of the viewport.

The clientY#dom-mouseevent-clientyReferenced in:10. Extensions to the MouseEvent Interface (2) (3) attribute must return the y-coordinate of the position where the event occurred relative to the origin of the viewport.

The x#dom-mouseevent-xReferenced in:10. Extensions to the MouseEvent Interface attribute must return the value of clientX.

The y#dom-mouseevent-yReferenced in:10. Extensions to the MouseEvent Interface attribute must return the value of clientY.

The offsetX#dom-mouseevent-offsetxReferenced in:10. Extensions to the MouseEvent Interface attribute must follow these steps:

  1. If the event’s dispatch flag is set, return the x-coordinate of the position where the event occurred relative to the origin of the padding edge of the target node, ignoring the transforms that apply to the element and its ancestors, and terminate these steps.

  2. Return the value of the event’s pageX attribute.

The offsetY#dom-mouseevent-offsetyReferenced in:10. Extensions to the MouseEvent Interface attribute must follow these steps:

  1. If the event’s dispatch flag is set, return the y-coordinate of the position where the event occurred relative to the origin of the padding edge of the target node, ignoring the transforms that apply to the element and its ancestors, and terminate these steps.

  2. Return the value of the event’s pageY attribute.

11. Geometry

11.1. The GeometryUtils Interface

enum CSSBoxType#enumdef-cssboxtypeReferenced in:11.1. The GeometryUtils Interface (2) (3) { "margin", "border", "padding", "content" };
dictionary BoxQuadOptions#dictdef-boxquadoptionsReferenced in:11.1. The GeometryUtils Interface {
  CSSBoxType box = "border";
  GeometryNode relativeTo; // XXX default document (i.e. viewport)
};

dictionary ConvertCoordinateOptions#dictdef-convertcoordinateoptionsReferenced in:11.1. The GeometryUtils Interface (2) (3) {
  CSSBoxType fromBox = "border";
  CSSBoxType toBox = "border";
};

[NoInterfaceObject]
interface GeometryUtils#geometryutilsReferenced in:11.1. The GeometryUtils Interface (2) (3) (4) (5) {
  sequence<DOMQuad> getBoxQuads(optional BoxQuadOptions options);
  DOMQuad convertQuadFromNode(DOMQuadInit quad, GeometryNode from, optional ConvertCoordinateOptions options);
  DOMQuad convertRectFromNode(DOMRectReadOnly rect, GeometryNode from, optional ConvertCoordinateOptions options);
  DOMPoint convertPointFromNode(DOMPointInit point, GeometryNode from, optional ConvertCoordinateOptions options); // XXX z,w turns into 0
};

Text implements GeometryUtils; // like Range
Element implements GeometryUtils;
CSSPseudoElement implements GeometryUtils;
Document implements GeometryUtils;

typedef (Text or Element or CSSPseudoElement or Document) GeometryNode#typedefdef-geometrynodeReferenced in:11.1. The GeometryUtils Interface (2) (3) (4);

The getBoxQuads(options)#dom-geometryutils-getboxquadsReferenced in:11.1. The GeometryUtils Interface method must run the following steps:

  1. DOM order

    p1 = top left even in RTL

    scale to 0 means divide by zero, return 0x0

    cross-frames not allowed, throw WrongDocumentError?

    points are flattened (3d transform), z=0. like getClientRect

    test block in inline

    pseudo-elements before/after are children of the element

    viewport boxes are all the same

The convertQuadFromNode(quad, from, options)#dom-geometryutils-convertquadfromnodeReferenced in:11.1. The GeometryUtils Interface method must run the following steps:

  1. ...

The convertRectFromNode(rect, from, options)#dom-geometryutils-convertrectfromnodeReferenced in:11.1. The GeometryUtils Interface method must run the following steps:

  1. ...

The convertPointFromNode(point, from, options)#dom-geometryutils-convertpointfromnodeReferenced in:11.1. The GeometryUtils Interface method must run the following steps:

  1. ...

12. Events

12.1. Resizing viewports

This section integrates with the event loop defined in HTML. [HTML]

When asked to run the resize steps for a Document doc, run these steps:

  1. If doc’s viewport has had its width or height changed (e.g. as a result of the user resizing the browser window, or changing the page zoom scale factor, or an iframe element’s dimensions are changed) since the last time these steps were run, fire an event named resize at the Window object associated with doc.

12.2. Scrolling

This section integrates with the event loop defined in HTML. [HTML]

Each Document has an associated list of pending scroll event targets#pending-scroll-event-targetsReferenced in:12.2. Scrolling (2) (3) (4) (5) (6), initially empty.

Whenever a viewport gets scrolled (whether in response to user interaction or by an API), the user agent must run these steps:

  1. Let doc be the viewport’s associated Document.

  2. If doc is already in doc’s pending scroll event targets, abort these steps.

  3. Append doc to doc’s pending scroll event targets.

Whenever an element gets scrolled (whether in response to user interaction or by an API), the user agent must run these steps:

  1. Let doc be the element’s node document.

  2. If the element is already in doc’s pending scroll event targets, abort these steps.

  3. Append the element to doc’s pending scroll event targets.

When asked to run the scroll steps for a Document doc, run these steps:

  1. For each item target in doc’s pending scroll event targets, in the order they were added to the list, run these substeps:

    1. If target is a Document, fire an event named scroll that bubbles at target.

    2. Otherwise, fire an event named scroll at target.

  2. Empty doc’s pending scroll event targets.

12.3. Event summary

This section is non-normative.

Event Interface Interesting targets Description
resize#eventdef-window-resizeReferenced in:12.1. Resizing viewportsChanges From 17 December 2013 Event Window Fired at the Window when the viewport is resized.
scroll#eventdef-document-scrollReferenced in:12.2. Scrolling (2)Changes From 17 December 2013 Event Document, elements Fired at the Document or element when the viewport or element is scrolled, respectively.

13. CSS properties

The features in this section should be moved to some other specification.

13.1. Smooth Scrolling: The scroll-behavior Property

Name: scroll-behavior#propdef-scroll-behaviorReferenced in:3.1. Scrolling (2)13.1. Smooth Scrolling: The scroll-behavior Property (2) (3)Changes From 17 December 2013Changes From 4 August 2011 To 17 December 2013
Value: auto | smooth
Initial: auto
Applies to: scrolling boxes
Inherited: no
Percentages: n/a
Media: visual
Computed value: specified value
Animatable: no
Canonical order: per grammar

The scroll-behavior property specifies the scrolling behavior for a scrolling box, when scrolling happens due to navigation or CSSOM scrolling APIs. Any other scrolls, e.g. those that are performed by the user, are not affected by this property. When this property is specified on the root element, it applies to the viewport instead.

The scroll-behavior property of the HTML body element is not propagated to the viewport.

auto#valdef-scroll-behavior-autoReferenced in:Changes From 17 December 2013
The scrolling box is scrolled in an instant fashion.
smooth#valdef-scroll-behavior-smoothReferenced in:3.1. Scrolling
The scrolling box is scrolled in a smooth fashion using a user-agent-defined timing function over a user-agent-defined period of time. User agents should follow platform conventions, if any.

User agents may ignore this property.

Change History

This section documents some of the changes between publications of this specification. This section is not exhaustive. Bug fixes and editorial changes are generally not listed.

Changes From 17 December 2013

Changes From 4 August 2011 To 17 December 2013

Acknowledgments

The editors would like to thank Alan Stearns, Alexey Feldgendler, Antonio Gomes, Björn Höhrmann, Boris Zbarsky, Chris Rebert, Dan Bates, David Vest, Elliott Sprehn, Garrett Smith, Henrik Andersson, Hallvord R. M. Steen, Kang-Hao Lu, Leif Arne Storset, Luiz Agostini, Maciej Stachowiak, Michael Dyck, Mike Wilson, Morten Stenshorne, Olli Pettay, Pavel Curtis, Peter-Paul Koch, Rachel Kmetz, Rick Byers, Robert O’Callahan, Sam Weinig, Scott Johnson, Sebastian Zartner, Stewart Brodie, Sylvain Galineau, Tab Atkins, Tarquin Wilton-Jones, Thomas Moore, Thomas Shinnick, and Xiaomei Ji for their contributions to this document.

Special thanks to the Microsoft employees who first implemented many of the features specified in this draft, which were first widely deployed by the Windows Internet Explorer browser.

Conformance

Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

Requirements for Responsible Implementation of CSS

The following sections define several conformance requirements for implementing CSS responsibly, in a way that promotes interoperability in the present and future.

Partial Implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported property values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

Implementations of Unstable and Proprietary Features

To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

Implementations of CR-level Features

Once a specification reaches the Candidate Recommendation stage, implementers should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec, and should avoid exposing a prefixed variant of that feature.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

[CSS-BACKGROUNDS-3]
CSS Backgrounds and Borders Module Level 3 URL: https://drafts.csswg.org/css-backgrounds-3/
[CSS-BREAK-3]
Rossen Atanassov; Elika Etemad. CSS Fragmentation Module Level 3. 14 January 2016. CR. URL: http://dev.w3.org/csswg/css-break/
[CSS-DEVICE-ADAPT]
Rune Lillesveen; Florian Rivoal; Matt Rakow. CSS Device Adaptation Module Level 1. 26 November 2015. WD. URL: http://www.w3.org/TR/css-device-adapt-1/
[CSS-DISPLAY-3]
Tab Atkins Jr.; Elika Etemad. CSS Display Module Level 3. 15 October 2015. WD. URL: http://dev.w3.org/csswg/css-display/
[CSS-OVERFLOW-4]
CSS Overflow Module Level 4 URL: https://drafts.csswg.org/css-overflow-4/
[CSS-POSITION-3]
CSS Positioned Layout Module Level 3 URL: https://drafts.csswg.org/css-position-3/
[CSS-PSEUDO-4]
Daniel Glazman; Elika Etemad; Alan Stearns. CSS Pseudo-Elements Module Level 4. 15 January 2015. WD. URL: http://dev.w3.org/csswg/css-pseudo-4/
[CSS-TRANSFORMS-1]
Simon Fraser; et al. CSS Transforms Module Level 1. 26 November 2013. WD. URL: http://www.w3.org/TR/css-transforms-1/
[CSS-VALUES]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 3. 11 June 2015. CR. URL: http://dev.w3.org/csswg/css-values/
[CSS-WRITING-MODES-3]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 3. 15 December 2015. CR. URL: http://dev.w3.org/csswg/css-writing-modes-3/
[CSS21]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. REC. URL: http://www.w3.org/TR/CSS2
[CSS3-BOX]
Bert Bos. CSS basic box model. 9 August 2007. WD. URL: http://www.w3.org/TR/css3-box
[CSSOM]
Simon Pieters; Glenn Adams. CSS Object Model (CSSOM). 5 December 2013. WD. URL: http://www.w3.org/TR/cssom/
[GEOMETRY-1]
Simon Pieters; Dirk Schulze; Rik Cabanier. Geometry Interfaces Module Level 1. 25 November 2014. CR. URL: http://dev.w3.org/fxtf/geometry/
[HTML]
Ian Hickson. HTML Standard. Living Standard. URL: https://html.spec.whatwg.org/multipage/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
[SVG]
Jon Ferraiolo. Scalable Vector Graphics (SVG) 1.0 Specification. 4 September 2001. REC. URL: http://www.w3.org/TR/SVG/
[WebIDL]
Cameron McCormack; Boris Zbarsky. WebIDL Level 1. 8 March 2016. CR. URL: http://www.w3.org/TR/WebIDL-1/
[WHATWG-DOM]
Anne van Kesteren. DOM Standard. Living Standard. URL: https://dom.spec.whatwg.org/

Informative References

[SVG2]
Nikos Andronikos; et al. Scalable Vector Graphics (SVG) 2. 15 September 2015. WD. URL: http://www.w3.org/TR/SVG2/

Property Index

Name Value Initial Applies to Inh. %ages Media Ani­mat­able Canonical order Com­puted value
scroll-behavior auto | smooth auto scrolling boxes no n/a visual no per grammar specified value

IDL Index

enum ScrollBehavior { "auto", "instant", "smooth" };

dictionary ScrollOptions {
    ScrollBehavior behavior = "auto";
};
dictionary ScrollToOptions : ScrollOptions {
    unrestricted double left;
    unrestricted double top;
};

partial interface Window {
    [NewObject] MediaQueryList matchMedia(DOMString query);
    [SameObject, Replaceable] readonly attribute Screen screen;

    // browsing context
    void moveTo(long x, long y);
    void moveBy(long x, long y);
    void resizeTo(long x, long y);
    void resizeBy(long x, long y);

    // viewport
    [Replaceable] readonly attribute long innerWidth;
    [Replaceable] readonly attribute long innerHeight;

    // viewport scrolling
    [Replaceable] readonly attribute double scrollX;
    [Replaceable] readonly attribute double pageXOffset;
    [Replaceable] readonly attribute double scrollY;
    [Replaceable] readonly attribute double pageYOffset;
    void scroll(optional ScrollToOptions options);
    void scroll(unrestricted double x, unrestricted double y);
    void scrollTo(optional ScrollToOptions options);
    void scrollTo(unrestricted double x, unrestricted double y);
    void scrollBy(optional ScrollToOptions options);
    void scrollBy(unrestricted double x, unrestricted double y);

    // client
    [Replaceable] readonly attribute long screenX;
    [Replaceable] readonly attribute long screenY;
    [Replaceable] readonly attribute long outerWidth;
    [Replaceable] readonly attribute long outerHeight;
    [Replaceable] readonly attribute double devicePixelRatio;
};

interface MediaQueryList : EventTarget {
  readonly attribute DOMString media;
  readonly attribute boolean matches;
  void addListener(EventListener? listener);
  void removeListener(EventListener? listener);
           attribute EventHandler onchange;
};

[Constructor(DOMString type, optional MediaQueryListEventInit eventInitDict)]
interface MediaQueryListEvent : Event {
  readonly attribute DOMString media;
  readonly attribute boolean matches;
};

dictionary MediaQueryListEventInit : EventInit {
  DOMString media = "";
  boolean matches = false;
};

interface Screen {
  readonly attribute long availWidth;
  readonly attribute long availHeight;
  readonly attribute long width;
  readonly attribute long height;
  readonly attribute unsigned long colorDepth;
  readonly attribute unsigned long pixelDepth;
};

partial interface Document {
  Element? elementFromPoint(double x, double y);
  sequence<Element> elementsFromPoint(double x, double y);
  CaretPosition? caretPositionFromPoint(double x, double y);
  readonly attribute Element? scrollingElement;
};

interface CaretPosition {
  readonly attribute Node offsetNode;
  readonly attribute unsigned long offset;
  [NewObject] DOMRect? getClientRect();
};

enum ScrollLogicalPosition { "start", "center", "end", "nearest" };
dictionary ScrollIntoViewOptions : ScrollOptions {
  ScrollLogicalPosition block = "center";
  ScrollLogicalPosition inline = "center";
};

partial interface Element {
  sequence<DOMRect> getClientRects();
  [NewObject] DOMRect getBoundingClientRect();
  void scrollIntoView();
  void scrollIntoView((boolean or object) arg);
  void scroll(optional ScrollToOptions options);
  void scroll(unrestricted double x, unrestricted double y);
  void scrollTo(optional ScrollToOptions options);
  void scrollTo(unrestricted double x, unrestricted double y);
  void scrollBy(optional ScrollToOptions options);
  void scrollBy(unrestricted double x, unrestricted double y);
  attribute unrestricted double scrollTop;
  attribute unrestricted double scrollLeft;
  readonly attribute long scrollWidth;
  readonly attribute long scrollHeight;
  readonly attribute long clientTop;
  readonly attribute long clientLeft;
  readonly attribute long clientWidth;
  readonly attribute long clientHeight;
};

partial interface HTMLElement {
  readonly attribute Element? offsetParent;
  readonly attribute long offsetTop;
  readonly attribute long offsetLeft;
  readonly attribute long offsetWidth;
  readonly attribute long offsetHeight;
};

partial interface HTMLImageElement {
  readonly attribute long x;
  readonly attribute long y;
};

partial interface Range {
  sequence<DOMRect> getClientRects();
  [NewObject] DOMRect getBoundingClientRect();
};

partial interface MouseEvent {
  readonly attribute double screenX;
  readonly attribute double screenY;
  readonly attribute double pageX;
  readonly attribute double pageY;
  readonly attribute double clientX;
  readonly attribute double clientY;
  readonly attribute double x;
  readonly attribute double y;
  readonly attribute double offsetX;
  readonly attribute double offsetY;
};

partial dictionary MouseEventInit {
  double screenX = 0.0;
  double screenY = 0.0;
  double clientX = 0.0;
  double clientY = 0.0;
};

enum CSSBoxType { "margin", "border", "padding", "content" };
dictionary BoxQuadOptions {
  CSSBoxType box = "border";
  GeometryNode relativeTo; // XXX default document (i.e. viewport)
};

dictionary ConvertCoordinateOptions {
  CSSBoxType fromBox = "border";
  CSSBoxType toBox = "border";
};

[NoInterfaceObject]
interface GeometryUtils {
  sequence<DOMQuad> getBoxQuads(optional BoxQuadOptions options);
  DOMQuad convertQuadFromNode(DOMQuadInit quad, GeometryNode from, optional ConvertCoordinateOptions options);
  DOMQuad convertRectFromNode(DOMRectReadOnly rect, GeometryNode from, optional ConvertCoordinateOptions options);
  DOMPoint convertPointFromNode(DOMPointInit point, GeometryNode from, optional ConvertCoordinateOptions options); // XXX z,w turns into 0
};

Text implements GeometryUtils; // like Range
Element implements GeometryUtils;
CSSPseudoElement implements GeometryUtils;
Document implements GeometryUtils;

typedef (Text or Element or CSSPseudoElement or Document) GeometryNode;

Issues Index

The terms CSS layout box and SVG layout box are not currently defined by CSS or SVG.
The object IDL fragment redefines some members. Can we resolve this somehow?
DOM order

p1 = top left even in RTL

scale to 0 means divide by zero, return 0x0

cross-frames not allowed, throw WrongDocumentError?

points are flattened (3d transform), z=0. like getClientRect

test block in inline

pseudo-elements before/after are children of the element

viewport boxes are all the same

...
...
...
The features in this section should be moved to some other specification.