SVG 2 – 28 August 2012 TopContentsPreviousNextElementsAttributesProperties

Appendix A: SVG Document Object Model (DOM)


This appendix is normative.

SVG 2 Requirement: Improve the DOM.
Resolution: We will generally improve the SVG DOM for SVG 2.
Purpose: Help authors use the SVG DOM by making it less Java-oriented.
Owner: Cameron (ACTION-3273)
Note: See SVG 2 DOM Wiki page.
SVG 2 Requirement: Improve the SVG path DOM APIs.
Resolution: We will improve the SVG path DOM APIs in SVG 2.
Purpose: Clean up SVGPathSegList interface, and possibly share an API with Canvas.
Owner: Cameron (no action)

A.1. SVG DOM overview

The SVG DOM is defined in terms of Web IDL interfaces. All IDL fragments in this specification must be interpreted as required for conforming IDL fragments, as described in the Web IDL specification. [WEBIDL]

The SVG DOM builds upon a number of DOM specifications. In particular:

A DOM application can use the hasFeature method of the DOMImplementation interface to verify that the interfaces listed in this section are supported. The list of available interfaces is provided in section Feature strings for the hasFeature method call.

All SVG DOM objects that directly correspond to an attribute, e.g. the SVGAnimatedLength ry in an SVGRectElement, are live. This means that any changes made to the attribute are immediately reflected in the corresponding SVG DOM object.

A.1.1. SVG DOM object initialization

The SVG DOM allows attributes to be accessed even though they haven't been specified explicitly in the document markup. When this happens an appropriate object is created, initialized and returned. This newly constructed object does not affect rendering until it is modified for the first time. After the first modification the object becomes live, such that any modifications made to the corresponding attribute are immediately reflected in the object.

For example, if rectElement.x.baseVal is accessed and the x attribute was not specified in the document, the returned SVG DOM object would represent the value 0 user units.

For cases where an attribute has a default value the returned SVG DOM object that must reflect that value, and for all other cases the object is initialized as described below. If a particular SVG DOM interface is not listed below that means that the object initialization shall be done using the values for the objects that the interface contains, e.g DOMString in the case of SVGAnimatedString, or four floats in the case of SVGRect.

Initialized with the return-value of getComputedTextLength on the same element.
Initialized as the empty string ("").
Initialized as 0.
Initialized as false.
Initialized as 0 user units (SVG_LENGTHTYPE_NUMBER).
Initialized as the empty list.
Initialized as 0 in unspecified units (SVG_ANGLETYPE_UNSPECIFIED).
Initialized as 0 (SVG_ZOOMANDPAN_UNKNOWN).
Initialized as 'xMidYMid meet'.

A.2. Elements in the SVG DOM

Every Element object that corresponds to an SVG element (that is, an element with namespace URI "" and a local name that is one of the elements defined in this specification) must also implement the DOM interface identified in element definition. For example, in The ‘rect’ element, the SVGRectElement interface is identified. This means that every Element object whose namespace URI is "" and whose local name is "rect" must also implement SVGRectElement.

A.3. Naming conventions

The SVG DOM follows similar naming conventions to the Document Object Model HTML ([DOM1], chapter 2).

All names are defined as one or more English words concatenated together to form a single string. Property or method names start with the initial keyword in lowercase, and each subsequent word starts with a capital letter. For example, a property that returns document meta information such as the date the file was created might be named "fileDateCreated". In the ECMAScript binding, properties are exposed as properties of a given object.

For attributes with the CDATA data type, the case of the return value is that given in the source document.

A.4. Feature strings for the hasFeature method call

The feature strings that are available for the hasFeature method call that is part of the SVG DOM's support for the DOMImplementation interface defined in DOM4 [DOM4] are the same features strings available for the requiredFeatures attribute that is available for many SVG elements.

For all features that correspond to the SVG language and are documented in this specification (see appendix Feature Strings for a list of features in the SVG language), the version number for the hasFeature method call is "1.1". For features that correspond to other languages, refer to the relevant other specifications to determine the appropriate version number for the given feature.

A.5. Relationship with DOM Level 2 Events

The SVG DOM supports all of the interfaces defined in, and the following event types from, DOM Level 2 Events [DOM2EVENTS]:

While event listeners can be registered using an addEventListener call on any element in the DOM, the use of event attributes on elements where those attributes are disallowed will not result in their being invoked if the relevant event is dispatched to the element. For example, if the onclick attribute were specified on a title element, its contents would never be run in response to a click event:

<svg xmlns="">
  <title onclick="alert('Hello')">Invalid event attribute</title>
    // Find the 'title' element.
    var title = document.getElementsByTagNameNS("", "title")[0];

    // Create and initialize a 'click' event.
    var event = document.createEvent("MouseEvent");
    event.initMouseEvent("click", true, false, this, 1, 0, 0, 0, 0, false,
                         false, false, false, 0, null);

    // Dispatch the event to the 'title' element.  Since onclick="" is not
    // allowed on 'title', the alert will not show.

See the Attribute Index for details on which elements a given event attribute is allowed to be specified on.

Implementors may view the setting of event attributes as the creation and registration of an EventListener on the EventTarget. Such event listeners are invoked only for the "bubbling" and "at target" phases, as if false were specified for the useCapture argument to addEventListener. This EventListener behaves in the same manner as any other which may be registered on the EventTarget.

If the attribute representing the event listener is changed, this may be viewed as the removal of the previously registered EventListener and the registration of a new one. Futhermore, no specification is made as to the order in which event attributes will receive the event with regards to the other EventListeners on the EventTarget.

In ECMAScript, one way to establish an event listener is to define a function and pass that function to the addEventListener method:

function myAction1(evt) {
  // process the event
// ... later ...
myElement.addEventListener("DOMActivate", myAction1, false)

In ECMAScript, the character data content of an event attribute becomes the definition of the ECMAScript function which gets invoked in response to the event. As with all registered ECMAScript event listener functions, this function receives an Event object as a parameter, and the name of the Event object is evt. For example, it is possible to write:

<rect onactivate="MyActivateHandler(evt)" .../>

which will pass the Event object evt into function MyActivateHandler.

A.6. Relationship with DOM Level 2 CSS

The section describes the facilities from DOM Level 2 CSS ([DOM2STYLE], chapter 2) that are part of the SVG DOM.

A.6.1. User agents that do not support styling with CSS

User agents that do not support styling with CSS are only required to support the following interfaces from DOM Level 2 CSS ([DOM2STYLE], chapter 2), along with any interfaces necessary to implement the interfaces, such as CSSPrimitiveValue and CSSValueList. These interfaces are used in conjunction with the getPresentationAttribute method call on interface SVGElement, which must be supported on all implementations of the SVG DOM.

A.6.2. User agents that support styling with CSS

User agents that support Styling with CSS, the SVG DOM, and aural styling ([CSS21], appendix A) must support all of the interfaces defined in DOM Level 2 CSS ([DOM2STYLE], chapter 2) which apply to aural properties.

For visual media ([CSS21], section 7.3.1), user agents must support all of the required interfaces defined in DOM Level 2 CSS. All of the interfaces that are optional for DOM Level 2 CSS are also optional for user agents implementing the SVG DOM.

A.6.3. Extended interfaces

Note: the getPresentationAttribute method and the interfaces that extend CSSValue are deprecated, and may be dropped from future versions of the SVG specification.

Whether or not a user agent supports styling with CSS, a user agent still must support interface CSSValue, as this is the type that is returned from the getPresentationAttribute method call on interface SVGElement.

DOM Level 2 CSS defines a set of extended interfaces ([DOM2STYLE], section 2.3) for use in conjunction with interface CSSValue. The table below specifies the type of CSSValue used to represent each SVG property that applies to visual media ([CSS21], section 7.3.1). The expectation is that the CSSValue returned from the getPropertyCSSValue method on the CSSStyleDeclaration interface or the getPresentationAttribute method on the SVGElement interface can be cast down, using binding-specific casting methods, to the specific derived interface.

For properties that are represented by a custom interface (the cssValueType of the CSSValue is CSS_CUSTOM), the name of the derived interface is specified in the table. For these properties, the table below indicates which extended interfaces are mandatory and which are not.

For properties that consist of lists of values (the cssValueType of the CSSValue is CSS_VALUE_LIST), the derived interface is CSSValueList. For all other properties (the cssValueType of the CSSValue is CSS_PRIMITIVE_VALUE), the derived interface is CSSPrimitiveValue.

For shorthand properties, a CSSValue always will have a value of null. Shorthand property values can only be accessed and modified as strings.

The SVG DOM defines the following SVG-specific custom property interfaces, all of which are mandatory for SVG user agents:

Property Name Representation Mandatory?
(Extended interfaces only)
alignment-baseline ident  
baseline-shift ident, length, percentage  
clip rect, ident  
clip-path uri, ident  
clip-rule ident  
color rgbcolor, ident  
color-interpolation ident  
color-rendering ident  
cursor uri, ident no
direction ident  
display ident  
dominant-baseline ident  
enable-background list of idents and numbers  
fill SVGPaint yes
fill-opacity number  
fill-rule ident  
filter uri, ident  
flood-color SVGColor yes
flood-opacity number  
font null  
font-family list of strings and idents  
font-size ident, length, percentage  
font-size-adjust number, ident  
font-stretch ident  
font-style ident  
font-variant ident  
font-weight ident  
glyph-orientation-horizontal ident  
glyph-orientation-vertical ident  
image-rendering ident  
letter-spacing ident, length  
lighting-color SVGColor yes
marker null  
marker-end uri, ident  
marker-mid uri, ident  
marker-start uri, ident  
mask uri, ident  
opacity number  
overflow ident  
pointer-events ident  
shape-rendering ident  
stop-color SVGColor yes
stop-opacity number  
stroke SVGPaint yes
stroke-dasharray ident or list of lengths  
stroke-dashoffset length  
stroke-linecap ident  
stroke-linejoin ident  
stroke-miterlimit length  
stroke-opacity number  
stroke-width length  
text-anchor ident  
text-decoration list of ident  
text-rendering ident  
unicode-bidi ident  
visibility ident  
word-spacing length, ident  
writing-mode ident  

A.7. Invalid values

If a script sets a DOM attribute to an invalid value (e.g., a negative number for an attribute that requires a non-negative number or an out-of-range value for an enumeration), unless this specification indicates otherwise, no exception shall be raised on setting, but the given document fragment shall become technically in error as described in Error processing.

SVG 2 – 28 August 2012 TopContentsPreviousNextElementsAttributesProperties