SVG usesstyling properties to describe many of its document parameters. Styling properties define how the graphics elements in the SVG content are to be rendered. SVG uses styling properties for the following:
SVG shares many of its styling properties with CSS [CSS2] and XSL [XSL]. Except for any additional SVG-specific rules explicitly mentioned in this specification, the normative definition of properties that are shared with CSS and XSL is the definition of the property from the CSS2 specification [CSS2].
The following properties are shared between CSS2 and SVG. Most of these properties are also defined in XSL:
The following SVG properties are not defined in [CSS2]. The complete normative definitions for these properties are found in this specification:
A table that lists and summarizes the styling properties can be found in theProperty Index.
SVG has many usage scenarios, each with different needs. Here are three common usage scenarios:
SVG content used as an exchange format (style sheet language-independent):
In some usage scenarios, reliable interoperability of SVG content across software tools is the main goal. Since support for a particular style sheet language is not guaranteed across all implementations, it is a requirement that SVG content can be fully specified without the use of a style sheet language.
SVG content generated as the output from XSLT [XSLT]:
XSLT offers the ability to take a stream of arbitrary XML content as input, apply potentially complex transformations, and then generate SVG content as output. XSLT can be used to transform XML data extracted from databases into an SVG graphical representation of that data. It is a requirement that fully specified SVG content can be generated from XSLT.
SVG content styled with CSS [CSS2]:
CSS is a widely implemented declarative language for assigning styling properties to XML content, including SVG. It represents a combination of features, simplicity and compactness that makes it very suitable for many applications of SVG. It is a requirement that CSS styling can be applied to SVG content.
Styling properties can be assigned to SVG elements in the following two ways:
Presentation attributes
Styling properties can be assigned using SVG'spresentation attributes. For each styling property defined in this specification, there is a corresponding XML presentation attribute available on all relevant SVG elements. Detailed information on the presentation attributes can be found inSpecifying properties using the presentation attributes.
The presentation attributes are style sheet language independent and thus are applicable to usage scenario 1 above (i.e., tool interoperability). Because it is straightforward to assign values to XML attributes from XSLT, the presentation attributes are well-suited to usage scenario 2 above (i.e., SVG generation from XSLT). (SeeStyling with XSL below.)
Conforming SVG Interpreters andConforming SVG Viewers are required to support SVG's presentation attributes.
CSS
To support usage scenario 3 above, SVG content can be styled with CSS. For more information, seeStyling with CSS.
Conforming SVG Interpreters andConforming SVG Viewers that support CSS styling of generic (i.e., text-based) XML content are required to support CSS styling of SVG content.
For each styling property defined in this specification (seeProperty Index), there is a corresponding XML attribute (thepresentation attribute) with the same name that is available on all relevant SVG elements. For example, SVG has a'fill' property that defines how to paint the interior of a shape. There is a corresponding presentation attribute with the same name (i.e.,fill) that can be used to specify a value for the'fill' property on a given element.
The following example shows how the'fill' and'stroke' properties can be assigned to a rectangle using thefill andstroke presentation attributes. The rectangle will be filled with red and outlined with blue:
<?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="10cm" height="5cm" viewBox="0 0 1000 500" xmlns="http://www.w3.org/2000/svg" version="1.1"> <rect x="200" y="100" width="600" height="300" fill="red" stroke="blue" stroke-width="3"/></svg>
View this example as SVG (SVG-enabled browsers only)
The presentation attributes offer the following advantages:
In some situations, SVG content that uses the presentation attributes has potential limitations versus SVG content that is styled with a style sheet language such as CSS (seeStyling with CSS). In other situations, such as when an XSLT style sheet generates SVG content from semantically rich XML source files, the limitations below may not apply. Depending on the situation, some of the following potential limitations may or may not apply to the presentation attributes:
For user agents that support CSS, the presentation attributes must be translated to corresponding CSS style rules according to rules described in section 6.4.4 of the CSS2 specification,Precedence of non-CSS presentational hints, with the additional clarification that the presentation attributes are conceptually inserted into a new author style sheet which is the first in the author style sheet collection. The presentation attributes thus will participate in theCSS2 cascade as if they were replaced by corresponding CSS style rules placed at the start of the author style sheet with a specificity of zero. In general, this means that the presentation attributes have lower priority than other CSS style rules specified in author style sheets orstyle attributes.
User agents that do not support CSS must ignore any CSS style rules defined in CSS style sheets andstyle attributes. In this case, the CSS cascade does not apply. (Inheritance of properties, however, does apply. SeeProperty inheritance.)
An!important declaration within a presentation attribute definition is an error.
Animation of presentation attributes is equivalent to animating the corresponding property. Thus, the same effect occurs from animating the presentation attribute withattributeType="XML" as occurs with animating the corresponding property withattributeType="CSS".
The following entities are defined in theDTD for all of the presentation attributes in SVG:
<!ENTITY %SVG.Core.attrib "" ><!ENTITY %SVG.Container.attrib "" ><!ENTITY %SVG.Conditional.attrib "" ><!ENTITY %SVG.Style.attrib "" ><!ENTITY %SVG.Viewport.attrib "" ><!ENTITY %SVG.Text.attrib "" ><!ENTITY %SVG.TextContent.attrib "" ><!ENTITY %SVG.Font.attrib "" ><!ENTITY %SVG.Paint.attrib "" ><!ENTITY %SVG.Color.attrib "" ><!ENTITY %SVG.Opacity.attrib "" ><!ENTITY %SVG.Graphics.attrib "" ><!ENTITY %SVG.Marker.attrib "" ><!ENTITY %SVG.Profile.attrib "" ><!ENTITY %SVG.Gradient.attrib "" ><!ENTITY %SVG.Clip.attrib "" ><!ENTITY %SVG.Mask.attrib "" ><!ENTITY %SVG.Filter.attrib "" ><!ENTITY %SVG.FilterColor.attrib "" ><!ENTITY %SVG.DocumentEvents.attrib "" ><!ENTITY %SVG.GraphicalEvents.attrib "" ><!ENTITY %SVG.Cursor.attrib "" ><!ENTITY %SVG.XLinkEmbed.attrib "" ><!ENTITY %SVG.External.attrib "" >
XSL style sheets (see [XSLT]) define how to transform XML content into something else, usually other XML. When XSLT is used in conjunction with SVG, sometimes SVG content will serve as both input and output for XSL style sheets. Other times, XSL style sheets will take non-SVG content as input and generate SVG content as output.
The following example uses an external XSL style sheet to transform SVG content into modified SVG content (seeReferencing external style sheets). The style sheet sets the'fill' and'stroke' properties on all rectangles to red and blue, respectively:
mystyle.xsl<?xml version="1.0" standalone="no"?><xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:svg="http://www.w3.org/2000/svg"> <xsl:output method="xml" encoding="utf-8" doctype-public="-//W3C//DTD SVG 1.1//EN" doctype-system="http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"/> <!-- Add version to topmost 'svg' element --> <xsl:template match="/svg:svg"> <xsl:copy> <xsl:copy-of select="@*"/> <xsl:attribute name="version">1.1</xsl:attribute> <xsl:apply-templates/> </xsl:copy> </xsl:template> <!-- Add styling to all 'rect' elements --> <xsl:template match="svg:rect"> <xsl:copy> <xsl:copy-of select="@*"/> <xsl:attribute name="fill">red</xsl:attribute> <xsl:attribute name="stroke">blue</xsl:attribute> <xsl:attribute name="stroke-width">3</xsl:attribute> </xsl:copy> </xsl:template></xsl:stylesheet>SVG file to be transformed by mystyle.xsl<?xml version="1.0" standalone="no"?><svg width="10cm" height="5cm" xmlns="http://www.w3.org/2000/svg"> <rect x="2cm" y="1cm" width="6cm" height="3cm"/></svg>SVG content after applying mystyle.xsl<?xml version="1.0" encoding="utf-8"?><!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"><svg width="10cm" height="5cm" version="1.1" xmlns="http://www.w3.org/2000/svg"> <rect x="2cm" y="1cm" width="6cm" height="3cm" fill="red" stroke="blue" stroke-width="3"/></svg>
SVG implementations that support CSS are required to support the following:
The following example shows the use of an external CSS style sheet to set the'fill' and'stroke' properties on all rectangles to red and blue, respectively:
mystyle.cssrect { fill: red; stroke: blue; stroke-width: 3}SVG file referencing mystyle.css<?xml version="1.0" standalone="no"?><?xml-stylesheet href="mystyle.css" type="text/css"?><!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"><svg width="10cm" height="5cm" viewBox="0 0 1000 500" xmlns="http://www.w3.org/2000/svg" version="1.1"> <rect x="200" y="100" width="600" height="300"/></svg>View this example as SVG (SVG-enabled browsers only)
CSS style sheets can be embedded within SVG content inside of a'style' element. The following example uses an internal CSS style sheet to achieve the same result as the previous example:
<?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="10cm" height="5cm" viewBox="0 0 1000 500" xmlns="http://www.w3.org/2000/svg" version="1.1"> <defs> <style type="text/css"><![CDATA[ rect { fill: red; stroke: blue; stroke-width: 3 } ]]></style> </defs> <rect x="200" y="100" width="600" height="300"/></svg>View this example as SVG (SVG-enabled browsers only)
Note how the CSS style sheet is placed within aCDATA construct (i.e.,<![CDATA[ ... ]]>). Placing internal CSS style sheets withinCDATA blocks is sometimes necessary since CSS style sheets can include characters, such as ">", which conflict with XML parsers. Even if a given style sheet does not use characters that conflict with XML parsing, it is highly recommended that internal style sheets be placed insideCDATA blocks.
Implementations that support CSS are also required to support CSS inline style. Similar to thestyle attribute in HTML, CSS inline style can be declared within astyle attribute in SVG by specifying a semicolon-separated list of property declarations, where each property declaration has the form "name: value".
The following example shows how the'fill' and'stroke' properties can be assigned to a rectangle using thestyle attribute. Just like the previous example, the rectangle will be filled with red and outlined with blue:
<?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="10cm" height="5cm" viewBox="0 0 1000 500" xmlns="http://www.w3.org/2000/svg" version="1.1"> <rect x="200" y="100" width="600" height="300" /></svg>
View this example as SVG (SVG-enabled browsers only)
In an SVG user agent that supports CSS style sheets, the following facilities from [CSS2] must be supported:
CDATA block.SVG defines an@color-profile at-rule [CSS2-ATRULES] for defining color profiles so that ICC color profiles can be applied to CSS-styled SVG content.
Note the following about relative URIs and external CSS style sheets: The CSS2 specification [CSS-URI] says that relative URIs (as defined in [RFC2396]) within style sheets are resolved such that the base URI is that of the style sheet, not that of the referencing document.
Property declarations viapresentation attributes are expressed in XML [XML10], which is case-sensitive. CSS property declarations specified either in CSS style sheets or in astyle attribute, on the other hand, are generally case-insensitive with some exceptions (see section4.1.3 Characters and case in the CSS2 specification).
Because presentation attributes are expressed as XML attributes, presentation attributes are case-sensitive and must match the exact name as listed under"Entity definitions for the presentation attributes", above. When using a presentation attribute to specify a value for the'fill' property, the presentation attribute must be specified as'fill' and not'FILL' or'Fill'. Keyword values, such as "italic" infont-style="italic", are also case-sensitive and must be specified using the exact case used in the specification which defines the given keyword. For example, the keyword "sRGB" must have lowercase "s" and uppercase "RGB".
Property declarations within CSS style sheets or in astyle attribute must only conform to CSS rules, which are generally more lenient with regard to case sensitivity. However, to promote consistency across the different ways for expressing styling properties, it is strongly recommended that authors use the exact property names (usually, lowercase letters and hyphens) as defined in the relevant specification and express all keywords using the same case as is required by presentation attributes and not take advantage of CSS's ability to ignore case.
SVG shares various relevant properties and approaches common to CSS and XSL, plus the semantics of many of the processing rules.
SVG shares the following facilities with CSS and XSL:
External style sheets are referenced using the mechanism documented in "Associating Style Sheets with XML documents Version 1.0" [XML-SS].
The'style' element allows style sheets to be embedded directly within SVG content. SVG's'style' element has the same attributes as the corresponding element in HTML (see HTML's'style' element).
<!ENTITY % SVG.style.extra.content "" ><!ENTITY % SVG.style.element "INCLUDE" ><![%SVG.style.element;[<!ENTITY % SVG.style.content "( #PCDATA %SVG.style.extra.content; )*"><!ELEMENT %SVG.style.qname; %SVG.style.content; ><!-- end of SVG.style.element -->]]><!ENTITY % SVG.style.attlist "INCLUDE" ><![%SVG.style.attlist;[<!ATTLIST %SVG.style.qname; xml:space ( preserve ) #FIXED 'preserve' %SVG.Core.attrib; type %ContentType.datatype; #REQUIRED media %MediaDesc.datatype; #IMPLIED title %Text.datatype; #IMPLIED> |
Attribute definitions:
The syntax of style data depends on the style sheet language.
Some style sheet languages might allow a wider variety of rules in the'style' element than in thestyle attribute. For example, with CSS, rules can be declared within a'style' element that cannot be declared within astyle attribute.
An example showing the'style' element is provided above (seeexample).
Attribute definitions:
Theclass attribute assigns one or more class names to an element. The element may be said to belong to these classes. A class name may be shared by several element instances. The class attribute has several roles:
In the following example, the'text' element is used in conjunction with theclass attribute to markup document messages. Messages appear in both English and French versions.
<!-- English messages --><text lang="en">Variable declared twice</text><text lang="en">Undeclared variable</text><text lang="en">Bad syntax for variable name</text><!-- French messages --><text lang="fr">Variable déclarée deux fois</text><text lang="fr">Variable indéfinie</text><text lang="fr">Erreur de syntaxe pour variable</text>
In an SVG user agent that supportsCSS styling, the following CSS style rules would tell visual user agents to display informational messages in green, warning messages in yellow, and error messages in red:
text.info { color: green }text.warning { color: yellow }text.error { color: red }Thestyle attribute allows per-element style rules to be specified directly on a given element. When CSS styling is used, CSS inline style is specified by including semicolon-separated property declarations of the form "name : value" within thestyle attribute
Attribute definitions:
The style attribute may be used to apply a particular style to an individual SVG element. If the style will be reused for several elements, authors should use the'style' element to regroup that information. For optimal flexibility, authors should define styles in external style sheets.
An example showing thestyle attribute is provided above (seeexample).
ThecontentStyleType attribute on the'svg' element specifies the default style sheet language for the given document fragment.
Whether or not the user agent supports CSS, property inheritance in SVG follows the property inheritance rules defined in the CSS2 specification. The normative definition for property inheritance is section 6.2 of the CSS2 specification (seeInheritance).
The definition of each property indicates whether the property can inherit the value of its parent.
In SVG, as in CSS2, most elements inherit computed values [ CSS2-COMPUTED]. For cases where something other than computed values are inherited, the property definition will describe the inheritance rules. For specified values [ CSS2-SPECIFIED] which are expressed in user units, in pixels (e.g., "20px") or in absolute values [ CSS2-COMPUTED], the computed value equals the specified value. For specified values which use certain relative units (i.e.,em,ex and percentages), the computed value will have the same units as the value to which it is relative. Thus, if the parent element has a'font-size' of "10pt" and the current element has a'font-size' of "120%", then the computed value for'font-size' on the current element will be "12pt". In cases where the referenced value for relative units is not expressed in any of the standard SVG units (i.e., CSS units or user units), such as when a percentage is used relative to the current viewport or an object bounding box, then the computed value will be in user units.
Note that SVG has some facilities wherein a property which is specified on an ancestor element might effect its descendant element, even if the descendant element has a different assigned value for that property. For example, if a'clip-path' property is specified on an ancestor element, and the current element has a'clip-path' of'none', the ancestor's clipping path still applies to the current element because the semantics of SVG state that the clipping path used on a given element is the intersection of all clipping paths specified on itself and all ancestor elements. The key concept is that property assignment (with possible property inheritance) happens first. After properties values have been assigned to the various elements, then the user agent applies the semantics of each assigned property, which might result in the property assignment of an ancestor element affecting the rendering of its descendants.
The following define the scope/range of style sheets:
The user agent shall maintain auser agent style sheet [CSS2-CASCADE-RULES] for elements in the SVG namespace for visual media [ CSS2-VISUAL]. The user agent style sheet below is expressed using CSS syntax; however, user agents are required to support the behavior that corresponds to this default style sheet even if CSS style sheets are not supported in the user agent:
svg, symbol, image, marker, pattern, foreignObject { overflow: hidden }svg { width:attr(width); height:attr(height) }The first line of the above user agent style sheet will cause theinitial clipping path to be established at the bounds of theinitial viewport. Furthermore, it will cause new clipping paths to be established at the bounds of the listed elements, all of which areelements that establish a new viewport. (Refer to the description of SVG's use of the'overflow' property for more information.)
The second line of the above user agent style sheet will cause thewidth andheight attributes on the'svg' element to be used as the default values for the 'width' and 'height' properties during [CSS2-LAYOUT].
For the purposes of aural media, SVG represents a stylable XML grammar. In user agents that support CSS aural style sheets, aural style properties [CSS2-AURAL] can be applied as defined in [CSS2].
Aural style properties can be applied to any SVG element that can contain character data content, including'desc','title,'tspan'.'tref'.'altGlyph' and'textPath'. On user agents that support aural style sheets, the following [CSS2] properties can be applied:
For user agents that support aural style sheets and also support [DOM2], the user agent is required to support the DOM interfaces defined in [DOM2-CSS] that correspond to aural properties [CSS2-AURAL]. (SeeRelationship with DOM2 CSS object model.)
| Elements | Attributes | Content Model |
|---|---|---|
| style | Core.attrib, type, media, title | (#PCDATA) |
The Style Module defines the Style.class content set.
| Content Set Name | Elements in Content Set |
|---|---|
| Style.class | style |
The Style Module defines the Style.attrib attribute set.
| Collection Name | Attributes in Collection |
|---|---|
| Style.attrib | style, class |
The following interfaces are defined below:SVGStyleElement.
TheSVGStyleElement interface corresponds to the'style' element.
interface SVGStyleElement : SVGElement { attribute DOMString xmlspace; // raises DOMException on setting attribute DOMString type; // raises DOMException on setting attribute DOMString media; // raises DOMException on setting attribute DOMString title; // raises DOMException on setting};| DOMException | NO_MODIFICATION_ALLOWED_ERR: Raised on an attempt to change the value of a readonly attribute. |
| DOMException | NO_MODIFICATION_ALLOWED_ERR: Raised on an attempt to change the value of a readonly attribute. |
| DOMException | NO_MODIFICATION_ALLOWED_ERR: Raised on an attempt to change the value of a readonly attribute. |
| DOMException | NO_MODIFICATION_ALLOWED_ERR: Raised on an attempt to change the value of a readonly attribute. |