17 Linking



17.1 Links out of SVG content: the 'a' element

SVG provides an 'a' element, analogous to like HTML's 'a' element, to indicate hyperlinks; those parts of the drawing which when clicked on will cause the current browser frame to be replaced by the contents of the URL specified in the href attribute.

Example link01 assigns a hyperlink to an ellipse.

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20000629//EN" 
<svg width="5cm" height="3cm">
  <desc>Example link01 - a hyperlink on an ellipse
  <rect x=".01cm" y=".01cm" width="4.98cm" height="2.98cm" 
        style="fill:none; stroke:blue"/>
  <a xlink:href="http://www.w3.org">
    <ellipse cx="2.5cm" cy="1.5cm" rx="2cm" ry="1cm"
Example link01
Example link01 - a hyperlink on an ellipse

View this example as SVG (SVG-enabled browsers only)

If the above SVG file is viewed by a user agent that supports both SVG and HTML, then clicking on the ellipse will cause the current window or frame to be replaced by the W3C home page.

<!ENTITY % aExt "" >
<!ELEMENT a       (#PCDATA|desc|title|metadata|defs|
                   %ceExt;%aExt;)* >
  xmlns:xlink CDATA #FIXED "http://www.w3.org/2000/xlink/namespace/"
  xlink:type (simple|extended|locator|arc) #FIXED "simple" 
  xlink:role CDATA #IMPLIED
  xlink:title CDATA #IMPLIED
  xlink:show (new|embed|replace) 'replace'
  xlink:actuate (onRequest|onLoad) #FIXED 'onRequest'
  xlink:href %URI; #REQUIRED
  externalResourcesRequired %Boolean; #IMPLIED
  class %ClassList; #IMPLIED
  style %StyleSheet; #IMPLIED
  transform %TransformList; #IMPLIED
  target %LinkTarget; #IMPLIED >

Attribute definitions:

xmlns [:prefix] = "resource-name"
Standard XML attribute for identifying an XML namespace. This attribute makes the XLink [XLink] namespace available to the current element. Refer to the "Namespaces in XML" Recommendation [XML-NS].
Animatable: no.
xlink:type = 'simple'
Identifies the type of XLink being used. For hyperlinks in SVG, only simple links are available. Refer to the "XML Linking Language (XLink)" [XLink].
Animatable: no.
xlink:role = '<string>'
A generic string used to describe the function of the link's content. Refer to the "XML Linking Language (XLink)" [XLink].
Animatable: no.
xlink:title = '<string>'
Human-readable text describing the link. Refer to the "XML Linking Language (XLink)" [XLink].
Animatable: no.
xlink:show = 'replace'
Indicates that upon activation of the link the referenced document will. replace the entire contents of the current document. Refer to the "XML Linking Language (XLink)" [XLink].
Animatable: no.
xlink:actuate = 'onRequest'
Indicates that the contents of the referenced object are incorporated into the current document upon user action. Refer to the "XML Linking Language (XLink)" [XLink].
Animatable: no.
xlink:href = "<uri>"
The location of the referenced object, expressed as a URI reference. Refer to the "XML Linking Language (XLink)" [XLink].
Animatable: yes.
target = "<frame-target>"
This attribute has applicability when the current SVG document is used as part of an HTML [HTML4] or XHTML [XHTML] parent document which defines multiple frames. This attribute specifies the name of an HTML or XHTML frame into which a document is to be opened when the hyperlink is activated. For more information, refer to the appropriate HTML or XHTML specifications.
Animatable: yes.
Attributes defined elsewhere:
%stdAttrs; %langSpaceAttrs;, class, transform, %graphicsElementEvents;, %testAttrs;, externalResourcesRequired style, %PresentationAttributes-All;.

17.2 Linking into SVG content: URI fragments and SVG views

17.2.1 Introduction: URI fragments and SVG views

On the Internet, resources are identified using URIs (Uniform Resource Identifiers) [URI]. For example, an SVG file called MyDrawing.svg located at http://www.MyCompany.com might have the following URI:


A URI can also address a particular element within an XML document by including a URI fragment identifier as part of the URI. A URI which includes a URI fragment identifier consists of an optional base URI, followed by a "#" character, followed by the URI fragment identifier. For example, the following URI can be used to specify the element whose ID is "Lamppost" within file MyDrawing.svg:


Because SVG content often represent a picture or drawing of something, a common need is to link into a particular view of the document, where a view indicates the initial transformations so as to present a closeup of a particular section of the document.

17.2.2 SVG fragment identifiers

To link into a particular view of an SVG document, the URI fragment identifier needs to be a correctly formed SVG fragment identifier. An SVG fragment identifier, which defines the meaning of the "selector" or "fragment identifier" portion of URIs that locate resources of MIME media type "image/svg".

An SVG fragment identifier can come in three forms:

An SVG fragment identifier is defined as follows:

SVGFragmentIdentifier ::= BareName |
                          XPointerIDRef |
BareName ::= XML_Name

XPointerIDRef ::= 'xpointer(id(' XML_Name '))'

SVGViewSpec ::= 'svgView(' SVGViewAttributes ')'

SVGViewAttributes ::= SVGViewAttribute |
                      SVGViewAttribute ';' SVGViewAttributes
SVGViewAttribute ::= viewBoxSpec |
                     preserveAspectRatioSpec |
                     transformSpec |
                     enableZoomAndPanControlsSpec |

viewBoxSpec ::= 'viewBox(' X ',' Y ',' Width ',' Height ')'

X ::= Number

Y ::= Number

Width ::= Number

Height ::= Number

preserveAspectRatioSpec = 'preserveAspectRatio(' AspectParams ')'

AspectParams ::= AspectValue |
                 AspectValue ',' MeetOrSlice

AspectValue ::= 'none' | 'xMinYMin' | 'xMinYMid' | 'xMinYMax' |
                'xMidYMin' | 'xMidYMid' | 'xMidYMax' |
                'xMaxYMin' | 'xMaxYMid' | 'xMaxYMax'

MeetOrSlice ::= 'meet' | 'slice'

Height ::= Number

transformSpec ::= 'transform(' TransformParams ')'

transformSpec ::= 'zoomAndPan(' TrueOrFalse ')'

TrueOrFalse ::= 'true' | 'false'

viewTargetSpec ::= 'viewTarget(' XML_Name ')'


Spaces are not allowed in fragment specifications; thus, commas are. used to separate numeric values within an SVG view specification (e.g., #svgView(viewBox(0,0,200,200))) and semicolons are. used to separate attributes (e.g., #svgView(viewBox(0,0,200,200);preserveAspectRatio(none))).

When a source document performs a hyperlink into an SVG document via an HTML [HTML4] linking element (i.e., <a href=...> element in HTML) or an XLink specification [XLINK], then the SVG fragment identifier specifies the initial view into the SVG document, as follows:

17.2.3 Predefined views: the 'view' element

The 'view' element is defined as follows:

<!ENTITY % viewExt "" >
<!ELEMENT view (%descTitleMetadata;%viewExt;) >
<!ATTLIST view
  externalResourcesRequired %Boolean; #IMPLIED
  viewBox %ViewBoxSpec; #IMPLIED
  preserveAspectRatio %PreserveAspectRatioSpec; 'xMidYMid meet'
  zoomAndPan (disable | magnify | zoom) 'magnify' 
  viewTarget CDATA #IMPLIED >

Attribute definitions:

viewTarget = "XML_Name [XML_NAME]*"
Indicates the target object associated with the view. If provided, then the target element(s) will. be highlighted.
Animatable: no.

Attributes defined elsewhere:
%stdAttrs;, viewBox, preserveAspectRatio, zoomAndPan externalResourcesRequired.

17.3 DOM interfaces

The following interfaces are defined below: SVGAElement, SVGViewElement.

Interface SVGAElement

The SVGAElement interface corresponds to the 'a' element.

IDL Definition
interface SVGAElement : 
                events::EventTarget { 

           attribute SVGAnimatedString target;
                       // raises DOMException on setting

SVGAnimatedString target
Corresponds to attribute target on the given 'a' element.
Exceptions on setting
NO_MODIFICATION_ALLOWED_ERR: Raised when the node is readonly.

Interface SVGViewElement

The SVGViewElement interface corresponds to the 'view' element.

IDL Definition
interface SVGViewElement : 
                SVGZoomAndPan { 

           attribute SVGElement viewTarget;
                       // raises DOMException on setting

SVGElement viewTarget
Corresponds to attribute viewTarget on the given 'view' element.
Exceptions on setting
NO_MODIFICATION_ALLOWED_ERR: Raised when the node is readonly.