On the Internet, resources are identified using IRIs (Internationalized Resource Identifiers). For example, an SVG file called someDrawing.svg located at http://example.com might have the following IRI:
http://example.com/someDrawing.svg
An IRI can also address a particular element within an XML document by including an IRI fragment identifier as part of the IRI. An IRI which includes an IRI fragment identifier consists of an optional base IRI, followed by a "#" character, followed by the IRI fragment identifier. For example, the following IRI can be used to specify the element whose ID is "Lamppost" within file someDrawing.svg:
http://example.com/someDrawing.svg#Lamppost
Internationalized Resource Identifiers (IRIs) are a more generalized complement to Uniform Resource Identifiers (URIs). An IRI is a sequence of characters from the Universal Character Set [UNICODE]. A URI is constructed from a much more restricted set of characters. All URIs are already conformant IRIs. A mapping from IRIs to URIs is defined by the IRI specification, which means that IRIs can be used instead of URIs in XML documents, to identify resources. IRIs can be converted to URIs for resolution on a network, if the protocol does not support IRIs directly.
Previous versions of SVG, following XLink, defined a IRI reference type as a URI or as a sequence of characters which must result in a URI reference after a particular escaping procedure was applied. The escaping procedure was repeated in the XLink 1.0 specification [XLINK], and in the W3C XML Schema Part 2: Datatypes specification [SCHEMA2]. This copying introduced the possibility of error and divergence, but was done because the IRI specification was not yet standardized.
In this specification, the correct term IRI is used for this "URI or sequence of characters plus an algorithm" and the escaping method, which turns IRIs into URIs, is defined by reference to the IRI specification [RFC3987], which has since become an IETF Proposed Standard. Other W3C specifications are expected to be revised over time to remove these duplicate descriptions of the escaping procedure and to refer to IRI directly.
IRIs are used in the ‘xlink:href’ attribute. Some attributes allow both IRIs and text strings as content. To disambiguate a text string from a relative IRI, the functional notation <FuncIRI> is used. This is simply an IRI delimited with a functional notation. Note: For historical reasons, the delimiters are "url(" and ")", for compatibility with the CSS specifications. The FuncIRI form is used in presentation attributes .
SVG makes extensive use of IRI references, both absolute and relative, to other objects. For example, to fill a rectangle with a linear gradient, you first define a ‘linearGradient’ element and give it an ID, as in:
<linearGradient xml:id="MyGradient">...</linearGradient>
You then reference the linear gradient as the value of the ‘fill’ property for the rectangle, as in the following example:
<rect fill="url(#MyGradient)"/>
SVG supports two types of IRI references:
The following rules apply to the processing of IRI references:
The following list describes the elements and properties that allow IRI references and the valid target types for those references:
The following rules apply to the processing of invalid IRI references:
IRI references are normally specified with an ‘href’ attribute in the XLink [XLink] namespace. For example, if the prefix of 'xlink' is used for attributes in the XLink namespace, then the attribute is be specified as ‘xlink:href’. The value of this attribute forms a reference for the desired resource (or secondary resource, if there is a fragment identifier).
The value of the ‘href’ attribute must be an Internationalized Resource Identifier.
If the protocol, such as HTTP, does not support IRIs directly, the IRI is converted to a URI by the SVG implementation, as described in section 3.1 of the IRI specification [RFC3987.
Because it is impractical for any application to check that a value is an IRI reference, this specification follows the lead of the IRI Specification in this matter and imposes no such conformance testing requirement on SVG applications.
If the IRI reference is relative, its absolute version must be computed by the method described in XML Base before use [XML-BASE].
Identifies the type of XLink being used. In SVG Tiny 1.2, only simple links are available. In line with the changes proposed in XLink 1.1 [XLINK11], this attribute may be omitted on simple links. Links are simple links by default, so the attribute xlink:type="simple" is optional and need not be explicitly stated. Refer to the XML Linking Language (XLink) [XLINK].
Animatable: no.
An optional IRI reference that identifies some resource that describes the intended property. The value must be an IRI reference as defined in [RFC3987], except that if the IRI scheme used is allowed to have absolute and relative forms, the IRI portion must be absolute. When no value is supplied, no particular role value shall be inferred. Refer to the XML Linking Language (XLink) [XLINK].
Animatable: no.
An optional IRI reference that identifies some resource that describes the intended property. The value must be an IRI reference as defined in [RFC3987], except that if the IRI scheme used is allowed to have absolute and relative forms, the IRI portion must be absolute. When no value is supplied, no particular role value shall be inferred. The arcrole attribute corresponds to the [RDF] notion of a property, where the role can be interpreted as stating that "starting-resource HAS arc-role ending-resource." This contextual role can differ from the meaning of an ending resource when taken outside the context of this particular arc. For example, a resource might generically represent a "person," but in the context of a particular arc it might have the role of "mother" and in the context of a different arc it might have the role of "daughter." Refer to the XML Linking Language (XLink) [XLINK].
Animatable: no.
The title attribute shall be used to describe the meaning of a link or resource in a human-readable fashion, along the same lines as the role or arcrole attribute. A value is optional; if a value is supplied, it shall contain a string that describes the resource. In general it is preferable to use a ‘title’ child element rather than a ‘title’ attribute. The use of this information is highly dependent on the type of processing being done. It may be used, for example, to make titles available to applications used by visually impaired users, or to create a table of links, or to present help text that appears when a user lets a mouse pointer hover over a starting resource. Refer to the XML Linking Language (XLink) [XLINK].
Animatable: no.
This attribute is provided for backwards compatibility with SVG 1.1. It provides documentation to XLink-aware processors. In case of a conflict, the target attribute has priority, since it can express a wider range of values. Refer to the XML Linking Language (XLink) [XLINK].
Animatable: no.
This attribute is provided for backwards compatibility with SVG 1.1. It provides documentation to XLink-aware processors. Refer to the XML Linking Language (XLink) [XLINK].
Animatable: no.
In all cases, for compliance with either the "Namespaces in XML 1.0" or the "Namespaces in XML 1.1" Recommendation [XML-NS10][XML-NS], an explicit XLink namespace declaration must be provided whenever one of the above XLink attributes is used within SVG content. One simple way to provide such an XLink namespace declaration is to include an ‘xmlns’ attribute for the XLink namespace on the ‘svg’ element for content that uses XLink attributes. For example:
<svg xmlns:xlink="http://www.w3.org/1999/xlink" ...> <image xlink:href="foo.png" .../> </svg>
SVG provides an ‘a’ element, to indicate links (also known as hyperlinks or Web links). The ‘a’ element may contain any element that its parent may contain, except itself.
SVG uses XLink ([XLink]) for all link definitions. SVG 1.1 only requires that user agents support XLink's notion of simple links. Each simple link associates exactly two resources, one local and one remote, with an arc going from the former to the latter.
A simple link is defined for each separate rendered element contained within the ‘a’ element; thus, if the ‘a’ element contains three ‘circle’ elements, a link is created for each circle. For each rendered element within an ‘a’ element, the given rendered element is the local resource (the source anchor for the link).
The remote resource (the destination for the link) is defined by a IRI specified by the XLink ‘xlink:href’ attribute on the ‘a’ element. The remote resource may be any Web resource (e.g., an image, a video clip, a sound bite, a program, another SVG document, an HTML document, an element within the current document, an element within a different document, etc.). By activating these links (by clicking with the mouse, through keyboard input, voice commands, etc.), users may visit these resources.
Example link01 assigns a link to an ellipse.
<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg width="5cm" height="3cm" viewBox="0 0 5 3" version="1.1"
xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<desc>Example link01 - a link on an ellipse
</desc>
<rect x=".01" y=".01" width="4.98" height="2.98"
fill="none" stroke="blue" stroke-width=".03"/>
<a xlink:href="http://www.w3.org">
<ellipse cx="2.5" cy="1.5" rx="2" ry="1"
fill="red" />
</a>
</svg> |
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.
Attribute definitions:
This attribute provides documentation to XLink-aware processors. If target="_blank" then use xlink:show="new" else use 'replace'. In case of a conflict, the target attribute has priority, since it can express a wider range of values. Refer to the XML Linking Language (XLink) [XLINK].
Animatable: no.
This attribute provides documentation to XLink-aware processors that an application should traverse from the starting resource to the ending resource only on a post-loading event triggered for the purpose of traversal. Refer to the XML Linking Language (XLink) [XLINK].
Animatable: no.
The location of the referenced object, expressed as an IRI reference.
Animatable: yes.
This attribute should be used when there are multiple possible targets for the ending resource, such as when the parent document is a multi-frame HTML or XHTML document. This attribute specifies the name or portion of the target window, frame, pane, tab, or other relevant presentation context (e.g., an HTML or XHTML frame, iframe, or object element) into which a document is to be opened when the link is activated. The values and semantics of this attribute are:
Note: The value '_new' is not a legal value for target (use '_blank').
Animatable: yes.
Because SVG content often represents 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.
To link into a particular view of an SVG document, the IRI fragment identifier needs to be a correctly formed SVG fragment identifier. An SVG fragment identifier defines the meaning of the "selector" or "fragment identifier" portion of IRIs that locate resources of MIME media type "image/svg+xml".
An SVG fragment identifier can come in two forms:
An SVG fragment identifier is defined as follows:
SVGFragmentIdentifier ::= BareName |
SVGViewSpec
BareName ::= XML_Name
SVGViewSpec ::= 'svgView(' SVGViewAttributes ')'
SVGViewAttributes ::= SVGViewAttribute |
SVGViewAttribute ';' SVGViewAttributes
SVGViewAttribute ::= viewBoxSpec |
preserveAspectRatioSpec |
transformSpec |
zoomAndPanSpec |
viewTargetSpec
viewBoxSpec ::= 'viewBox(' ViewBoxParams ')'
preserveAspectRatioSpec = 'preserveAspectRatio(' AspectParams ')'
transformSpec ::= 'transform(' TransformParams ')'
zoomAndPanSpec ::= 'zoomAndPan(' ZoomAndPanParams ')'
viewTargetSpec ::= 'viewTarget(' ViewTargetParams ')'
where:
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 link into an SVG document, for example via an HTML anchor element ([HTML4], section 12.2; 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:
The ‘view’ element is defined as follows:
Attribute definitions:
interface SVGAElement : SVGElement,
SVGURIReference,
SVGTests,
SVGLangSpace,
SVGExternalResourcesRequired,
SVGStylable,
SVGTransformable {
readonly attribute SVGAnimatedString target;
};interface SVGViewElement : SVGElement,
SVGExternalResourcesRequired,
SVGFitToViewBox,
SVGZoomAndPan {
readonly attribute SVGStringList viewTarget;
};