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Scalable Vector Graphics (SVG) 1.1 (Second Edition)1 Introduction1.1 About SVG1.2 SVG MIME type1.3 SVG Namespace1.4 Compatibility with Other Standards Efforts1.5 Terminology1.6 Definitions2 Concepts2.1 Explaining the name: SVG2.2 Important SVG concepts2.3 Options for using SVG in Web pages3 Rendering Model3.1 Introduction3.2 The painters model3.3 Rendering Order3.4 How groups are rendered3.5 How elements are rendered3.6 Types of graphics elements3.6.1 Painting shapes and text3.6.2 Painting raster images3.7 Filtering painted regions3.8 Clipping3.9 Parent Compositing4 Basic Data Types and Interfaces4.1 Syntax4.2 Basic data types4.3 Real number precision4.4 Recognized color keyword names4.5 Basic DOM interfaces4.5.1 Interface SVGElement4.5.2 Interface SVGAnimatedBoolean4.5.3 Interface SVGAnimatedString4.5.4 Interface SVGStringList4.5.5 Interface SVGAnimatedEnumeration4.5.6 Interface SVGAnimatedInteger4.5.7 Interface SVGNumber4.5.8 Interface SVGAnimatedNumber4.5.9 Interface SVGNumberList4.5.10 Interface SVGAnimatedNumberList4.5.11 Interface SVGLength4.5.12 Interface SVGAnimatedLength4.5.13 Interface SVGLengthList4.5.14 Interface SVGAnimatedLengthList4.5.15 Interface SVGAngle4.5.16 Interface SVGAnimatedAngle4.5.17 Interface SVGColor4.5.18 Interface SVGICCColor4.5.19 Interface SVGRect4.5.20 Interface SVGAnimatedRect4.5.21 Interface SVGUnitTypes4.5.22 Interface SVGStylable4.5.23 Interface SVGLocatable4.5.24 Interface SVGTransformable4.5.25 Interface SVGTests4.5.26 Interface SVGLangSpace4.5.27 Interface SVGExternalResourcesRequired4.5.28 Interface SVGFitToViewBox4.5.29 Interface SVGZoomAndPan4.5.30 Interface SVGViewSpec4.5.31 Interface SVGURIReference4.5.32 Interface SVGCSSRule4.5.33 Interface SVGRenderingIntent5 Document Structure5.1 Defining an SVG document fragment: the 憇vg?element5.1.1 Overview5.1.2 The 憇vg?element5.2 Grouping: the 慻?element5.2.1 Overview5.2.2 The 慻?element5.3 Defining content for reuse5.3.1 Overview5.3.2 The 慸efs?element5.4 The 慸esc?and 憈itle?elements5.5 The 憇ymbol?element5.6 The 憉se?element5.7 The 慽mage?element5.8 Conditional processing5.8.1 Conditional processing overview5.8.2 The 憇witch?element5.8.3 The 憆equiredFeatures?attribute5.8.4 The 憆equiredExtensions?attribute5.8.5 The 憇ystemLanguage?attribute5.8.6 Applicability of test attributes5.9 Specifying whether external resources are required for proper rendering5.10 Common attributes5.10.1 Attributes common to all elements: 慽d?and 憍ml:base?5.10.2 The 憍ml:lang?and 憍ml:space?attributes5.11 DOM interfaces5.11.1 Interface SVGDocument5.11.2 Interface SVGSVGElement5.11.3 Interface SVGGElement5.11.4 Interface SVGDefsElement5.11.5 Interface SVGDescElement5.11.6 Interface SVGTitleElement5.11.7 Interface SVGSymbolElement5.11.8 Interface SVGUseElement5.11.9 Interface SVGElementInstance5.11.10 Interface SVGElementInstanceList5.11.11 Interface SVGImageElement5.11.12 Interface SVGSwitchElement5.11.13 Interface GetSVGDocument6 Styling6.1 SVG's styling properties6.2 Usage scenarios for styling6.3 Alternative ways to specify styling properties6.4 Specifying properties using the presentation attributes6.5 Styling with XSL6.6 Styling with CSS6.7 Case sensitivity of property names and values6.8 Facilities from CSS and XSL used by SVG6.9 Referencing external style sheets6.10 The 憇tyle?element6.11 The 慶lass?attribute6.12 The 憇tyle?attribute6.13 Specifying the default style sheet language6.14 Property inheritance6.15 The scope/range of styles6.16 User agent style sheet6.17 Aural style sheets6.18 DOM interfaces6.18.1 Interface SVGStyleElement7 Coordinate Systems7.1 Introduction7.2 The initial viewport7.3 The initial coordinate system7.4 Coordinate system transformations7.5 Nested transformations7.6 The 憈ransform?attribute7.7 The 憊iewBox?attribute7.8 The 憄reserveAspectRatio?attribute7.9 Establishing a new viewport7.10 Units7.11 Object bounding box units7.12 Intrinsic sizing properties of the viewport of SVG content7.13 Geographic coordinate systems7.14 The 憇vg:transform?attribute7.15 DOM interfaces7.15.1 Interface SVGPoint7.15.2 Interface SVGPointList7.15.3 Interface SVGMatrix7.15.4 Interface SVGTransform7.15.5 Interface SVGTransformList7.15.6 Interface SVGAnimatedTransformList7.15.7 Interface SVGPreserveAspectRatio7.15.8 Interface SVGAnimatedPreserveAspectRatio8 Paths8.1 Introduction8.2 The 憄ath?element8.3 Path data8.3.1 General information about path data8.3.2 The "moveto" commands8.3.3 The "closepath" command8.3.4 The "lineto" commands8.3.5 The curve commands8.3.6 The cubic B閦ier curve commands8.3.7 The quadratic B閦ier curve commands8.3.8 The elliptical arc curve commands8.3.9 The grammar for path data8.4 Distance along a path8.5 DOM interfaces8.5.1 Interface SVGPathSeg8.5.2 Interface SVGPathSegClosePath8.5.3 Interface SVGPathSegMovetoAbs8.5.4 Interface SVGPathSegMovetoRel8.5.5 Interface SVGPathSegLinetoAbs8.5.6 Interface SVGPathSegLinetoRel8.5.7 Interface SVGPathSegCurvetoCubicAbs8.5.8 Interface SVGPathSegCurvetoCubicRel8.5.9 Interface SVGPathSegCurvetoQuadraticAbs8.5.10 Interface SVGPathSegCurvetoQuadraticRel8.5.11 Interface SVGPathSegArcAbs8.5.12 Interface SVGPathSegArcRel8.5.13 Interface SVGPathSegLinetoHorizontalAbs8.5.14 Interface SVGPathSegLinetoHorizontalRel8.5.15 Interface SVGPathSegLinetoVerticalAbs8.5.16 Interface SVGPathSegLinetoVerticalRel8.5.17 Interface SVGPathSegCurvetoCubicSmoothAbs8.5.18 Interface SVGPathSegCurvetoCubicSmoothRel8.5.19 Interface SVGPathSegCurvetoQuadraticSmoothAbs8.5.20 Interface SVGPathSegCurvetoQuadraticSmoothRel8.5.21 Interface SVGPathSegList8.5.22 Interface SVGAnimatedPathData8.5.23 Interface SVGPathElement9 Basic Shapes9.1 Introduction9.2 The 憆ect?element9.3 The 慶ircle?element9.4 The 慹llipse?element9.5 The 憀ine?element9.6 The 憄olyline?element9.7 The 憄olygon?element9.7.1 The grammar for points specifications in 憄olyline?and 憄olygon?elements9.8 DOM interfaces9.8.1 Interface SVGRectElement9.8.2 Interface SVGCircleElement9.8.3 Interface SVGEllipseElement9.8.4 Interface SVGLineElement9.8.5 Interface SVGAnimatedPoints9.8.6 Interface SVGPolylineElement9.8.7 Interface SVGPolygonElement10 Text10.1 Introduction10.2 Characters and their corresponding glyphs10.3 Fonts10.4 The 憈ext?element10.5 The 憈span?element10.6 The 憈ref?element10.7 Text layout10.7.1 Text layout introduction10.7.2 Setting the inline-progression-direction10.7.3 Glyph orientation within a text run10.7.4 Relationship with bidirectionality10.8 Text rendering order10.9 Alignment properties10.9.1 Text alignment properties10.9.2 Baseline alignment properties10.10 Font selection properties10.11 Spacing properties10.12 Text decoration10.13 Text on a path10.13.1 Introduction to text on a path10.13.2 The 憈extPath?element10.13.3 Text on a path layout rules10.14 Alternate glyphs10.14.1 The 慳ltGlyph?element10.14.2 The 慳ltGlyphDef? 慳ltGlyphItem?and 慻lyphRef?elements10.15 White space handling10.16 Text selection and clipboard operations10.17 DOM interfaces10.17.1 Interface SVGTextContentElement10.17.2 Interface SVGTextPositioningElement10.17.3 Interface SVGTextElement10.17.4 Interface SVGTSpanElement10.17.5 Interface SVGTRefElement10.17.6 Interface SVGTextPathElement10.17.7 Interface SVGAltGlyphElement10.17.8 Interface SVGAltGlyphDefElement10.17.9 Interface SVGAltGlyphItemElement10.17.10 Interface SVGGlyphRefElement11 Painting: Filling11.1 Introduction11.2 Specifying paint11.3 Fill Properties11.4 Stroke Properties11.5 Controlling visibility11.6 Markers11.6.1 Introduction11.6.2 The 憁arker?element11.6.3 Marker properties11.6.4 Details on how markers are rendered11.7 Rendering properties11.7.1 Color interpolation properties: 慶olor-interpolation?and 慶olor-interpolation-filters?11.7.2 The 慶olor-rendering?property11.7.3 The 憇hape-rendering?property11.7.4 The 憈ext-rendering?property11.7.5 The 慽mage-rendering?property11.8 Inheritance of painting properties11.9 DOM interfaces11.9.1 Interface SVGPaint11.9.2 Interface SVGMarkerElement12 Color12.1 Introduction12.2 The 慶olor?property12.3 Color profile descriptions12.3.1 Overview of color profile descriptions12.3.2 Alternative ways of defining a color profile description12.3.3 The 慶olor-profile?element12.3.4 The CSS @color-profile rule12.3.5 The 慶olor-profile?property12.4 DOM interfaces12.4.1 Interface SVGColorProfileElement12.4.2 Interface SVGColorProfileRule13 Gradients and Patterns13.1 Introduction13.2 Gradients13.2.1 Introduction13.2.2 Linear gradients13.2.3 Radial gradients13.2.4 Gradient stops13.3 Patterns13.4 DOM interfaces13.4.1 Interface SVGGradientElement13.4.2 Interface SVGLinearGradientElement13.4.3 Interface SVGRadialGradientElement13.4.4 Interface SVGStopElement13.4.5 Interface SVGPatternElement14 Clipping14.1 Introduction14.2 Simple alpha compositing14.3 Clipping paths14.3.1 Introduction14.3.2 The initial clipping path14.3.3 The 憃verflow?and 慶lip?properties14.3.4 Clip to viewport vs. clip to 憊iewBox?14.3.5 Establishing a new clipping path: the 慶lipPath?element14.3.6 Clipping paths14.4 Masking14.5 Object and group opacity: the 憃pacity?property14.6 DOM interfaces14.6.1 Interface SVGClipPathElement14.6.2 Interface SVGMaskElement15 Filter Effects15.1 Introduction15.2 An example15.3 The 慺ilter?element15.4 The 慺ilter?property15.5 Filter effects region15.6 Accessing the background image15.7 Filter primitives overview15.7.1 Overview15.7.2 Common attributes15.7.3 Filter primitive subregion15.8 Light source elements and properties15.8.1 Introduction15.8.2 Light source 慺eDistantLight?15.8.3 Light source 慺ePointLight?15.8.4 Light source 慺eSpotLight?15.8.5 The 憀ighting-color?property15.9 Filter primitive 慺eBlend?15.10 Filter primitive 慺eColorMatrix?15.11 Filter primitive 慺eComponentTransfer?15.12 Filter primitive 慺eComposite?15.13 Filter primitive 慺eConvolveMatrix?15.14 Filter primitive 慺eDiffuseLighting?15.15 Filter primitive 慺eDisplacementMap?15.16 Filter primitive 慺eFlood?15.17 Filter primitive 慺eGaussianBlur?15.18 Filter primitive 慺eImage?15.19 Filter primitive 慺eMerge?15.20 Filter primitive 慺eMorphology?15.21 Filter primitive 慺eOffset?15.22 Filter primitive 慺eSpecularLighting?15.23 Filter primitive 慺eTile?15.24 Filter primitive 慺eTurbulence?15.25 DOM interfaces15.25.1 Interface SVGFilterElement15.25.2 Interface SVGFilterPrimitiveStandardAttributes15.25.3 Interface SVGFEBlendElement15.25.4 Interface SVGFEColorMatrixElement15.25.5 Interface SVGFEComponentTransferElement15.25.6 Interface SVGComponentTransferFunctionElement15.25.7 Interface SVGFEFuncRElement15.25.8 Interface SVGFEFuncGElement15.25.9 Interface SVGFEFuncBElement15.25.10 Interface SVGFEFuncAElement15.25.11 Interface SVGFECompositeElement15.25.12 Interface SVGFEConvolveMatrixElement15.25.13 Interface SVGFEDiffuseLightingElement15.25.14 Interface SVGFEDistantLightElement15.25.15 Interface SVGFEPointLightElement15.25.16 Interface SVGFESpotLightElement15.25.17 Interface SVGFEDisplacementMapElement15.25.18 Interface SVGFEFloodElement15.25.19 Interface SVGFEGaussianBlurElement15.25.20 Interface SVGFEImageElement15.25.21 Interface SVGFEMergeElement15.25.22 Interface SVGFEMergeNodeElement15.25.23 Interface SVGFEMorphologyElement15.25.24 Interface SVGFEOffsetElement15.25.25 Interface SVGFESpecularLightingElement15.25.26 Interface SVGFETileElement15.25.27 Interface SVGFETurbulenceElement16 Interactivity16.1 Introduction16.2 Complete list of supported events16.3 User interface events16.4 Pointer events16.5 Hit-testing and processing order for user interface events16.5.1 Hit-testing16.5.2 Event processing16.6 The 憄ointer-events?property16.7 Magnification and panning16.8 Cursors16.8.1 Introduction to cursors16.8.2 The 慶ursor?property16.8.3 The 慶ursor?element16.9 DOM interfaces16.9.1 Interface SVGCursorElement17 Linking17.1 References17.1.1 Overview17.1.2 IRIs and URIs17.1.3 Syntactic forms: IRI and FuncIRI17.1.4 Processing of IRI references17.1.5 IRI reference attributes17.2 Links out of SVG content: the 慳?element17.3 Linking into SVG content: IRI fragments and SVG views17.3.1 Introduction: IRI fragments and SVG views17.3.2 SVG fragment identifiers17.3.3 Predefined views: the 憊iew?element17.3.4 Highlighting views17.4 DOM interfaces17.4.1 Interface SVGAElement17.4.2 Interface SVGViewElement18 Scripting18.1 Specifying the scripting language18.1.1 Specifying the default scripting language18.1.2 Local declaration of a scripting language18.2 The 憇cript?element18.3 Event handling18.4 Event attributes18.4.1 Event attribute for the SVGLoad event18.4.2 Event attributes on graphics and container elements18.4.3 Document-level event attributes18.4.4 Animation event attributes18.5 DOM interfaces18.5.1 Interface SVGScriptElement18.5.2 Interface SVGZoomEvent19 Animation19.1 Introduction19.2 Animation elements19.2.1 Overview19.2.2 Relationship to SMIL Animation19.2.3 Animation elements example19.2.4 Attributes to identify the target element for an animation19.2.5 Attributes to identify the target attribute or property for an animation19.2.6 Animation with namespaces19.2.7 Paced animation and complex types19.2.8 Attributes to control the timing of the animation19.2.8.1 Clock values19.2.9 Attributes that define animation values over time19.2.10 Attributes that control whether animations are additive19.2.11 Inheritance19.2.12 The 慳nimate?element19.2.13 The 憇et?element19.2.14 The 慳nimateMotion?element19.2.15 The 慳nimateColor?element19.2.16 The 慳nimateTransform?element19.2.17 Elements19.3 Animation using the SVG DOM19.4 DOM interfaces19.4.1 Interface ElementTimeControl19.4.2 Interface TimeEvent19.4.3 Interface SVGAnimationElement19.4.4 Interface SVGAnimateElement19.4.5 Interface SVGSetElement19.4.6 Interface SVGAnimateMotionElement19.4.7 Interface SVGMPathElement19.4.8 Interface SVGAnimateColorElement19.4.9 Interface SVGAnimateTransformElement20 Fonts20.1 Introduction20.2 Overview of SVG fonts20.3 The 慺ont?element20.4 The 慻lyph?element20.5 The 憁issing-glyph?element20.6 Glyph selection rules20.7 The 慼kern?and 憊kern?elements20.8 Describing a font20.8.1 Overview of font descriptions20.8.2 Alternative ways for providing a font description20.8.3 The 慺ont-face?element20.8.4 The 慺ont-face-src?element20.8.5 The 慺ont-face-uri?and 慺ont-face-format?elements20.8.6 The 慺ont-face-name?element20.9 DOM interfaces20.9.1 Interface SVGFontElement20.9.2 Interface SVGGlyphElement20.9.3 Interface SVGMissingGlyphElement20.9.4 Interface SVGHKernElement20.9.5 Interface SVGVKernElement20.9.6 Interface SVGFontFaceElement20.9.7 Interface SVGFontFaceSrcElement20.9.8 Interface SVGFontFaceUriElement20.9.9 Interface SVGFontFaceFormatElement20.9.10 Interface SVGFontFaceNameElement21 Metadata21.1 Introduction21.2 The 憁etadata?element21.3 An example21.4 DOM interfaces21.4.1 Interface SVGMetadataElement22 Backwards Compatibility23 Extensibility23.1 Foreign namespaces and private data23.2 Embedding foreign object types23.3 The 慺oreignObject?element23.4 An example23.5 Adding private elements and attributes to the DTD23.6 DOM interfaces23.6.1 Interface SVGForeignObjectElementAppendix A: Document Type DefinitionA.1 IntroductionA.2 ModularizationA.2.1 Element and attribute collectionsA.2.2 Profiling the SVG specificationA.2.3 Practical considerationsA.3 SVG 1.1 module definitions and DTD implementationsA.3.1 Modular Framework ModuleA.3.2 Datatypes ModuleA.3.3 Qualified Name ModuleA.3.4 Core Attribute ModuleA.3.5 Container Attribute ModuleA.3.6 Viewport Attribute ModuleA.3.7 Paint Attribute ModuleA.3.8 Basic Paint Attribute ModuleA.3.9 Paint Opacity Attribute ModuleA.3.10 Graphics Attribute ModuleA.3.11 Basic Graphics Attribute ModuleA.3.12 Document Events Attribute ModuleA.3.13 Graphical Element Events Attribute ModuleA.3.14 Animation Events Attribute ModuleA.3.15 XLink Attribute ModuleA.3.16 External Resources Attribute ModuleA.3.17 Structure ModuleA.3.18 Basic Structure ModuleA.3.19 Conditional Processing ModuleA.3.20 Image ModuleA.3.21 Style ModuleA.3.22 Shape ModuleA.3.23 Text ModuleA.3.24 Basic Text ModuleA.3.25 Marker ModuleA.3.26 Color Profile ModuleA.3.27 Gradient ModuleA.3.28 Pattern ModuleA.3.29 Clip ModuleA.3.30 Basic Clip ModuleA.3.31 Mask ModuleA.3.32 Filter ModuleA.3.33 Basic Filter ModuleA.3.34 Cursor ModuleA.3.35 Hyperlinking ModuleA.3.36 View ModuleA.3.37 Scripting ModuleA.3.38 Animation ModuleA.3.39 Font ModuleA.3.40 Basic Font ModuleA.3.41 Extensibility ModuleA.4 SVG 1.1 Document Type DefinitionA.4.1 SVG 1.1 DTD DriverA.4.2 SVG 1.1 Document ModelA.4.3 SVG 1.1 Attribute CollectionAppendix B: SVG Document Object Model (DOM)B.1 SVG DOM overviewB.1.1 SVG DOM object initializationB.2 Elements in the SVG DOMB.3 Naming conventionsB.4 Exception SVGExceptionB.5 Feature strings for the hasFeature method callB.6 Relationship with DOM Level 2 EventsB.7 Relationship with DOM Level 2 CSSB.7.1 IntroductionB.7.2 User agents that do not support styling with CSSB.7.3 User agents that support styling with CSSB.7.4 Extended interfacesB.8 Read only nodes in the DOMB.9 Invalid valuesAppendix C: IDL DefinitionsAppendix D: Java Language BindingD.1 The Java language bindingD.2 Using SVG with the Java languageAppendix E: ECMAScript Language BindingE.1 ExceptionsE.2 ConstantsE.3 TypesE.4 ObjectsAppendix F: Implementation RequirementsF.1 IntroductionF.2 Error processingF.3 Version controlF.4 Clamping values which are restricted to a particular rangeF.5 憄ath?element implementation notesF.6 Elliptical arc implementation notesF.6.1 Elliptical arc syntaxF.6.2 Out-of-range parametersF.6.3 Parameterization alternativesF.6.4 Conversion from center to endpoint parameterizationF.6.5 Conversion from endpoint to center parameterizationF.6.6 Correction of out-of-range radiiF.7 Text selection implementation notesF.8 Printing implementation notesAppendix G: Conformance CriteriaG.1 IntroductionG.2 Conforming SVG Document FragmentsG.3 Conforming SVG Stand-Alone FilesG.4 Conforming SVG GeneratorsG.5 Conforming SVG ServersG.6 Conforming SVG DOM SubtreeG.7 Conforming SVG InterpretersG.8 Conforming SVG ViewersAppendix H: Accessibility SupportH.1 WAI Accessibility GuidelinesH.2 SVG Content Accessibility GuidelinesAppendix I: Internationalization SupportI.1 IntroductionI.2 Internationalization and SVGI.3 SVG Internationalization GuidelinesAppendix J: Minimizing SVG File SizesAppendix K: ReferencesK.1 Normative referencesK.2 Informative referencesAppendix L: Element IndexAppendix M: Attribute IndexM.1 Regular attributesM.2 Presentation attributesAppendix N: Property IndexAppendix O: Feature StringsO.1 IntroductionO.2 SVG 1.1 feature stringsO.3 SVG 1.0 feature stringsAppendix P: Media Type Registration for image/svg+xmlP.1 IntroductionP.2 Registration of media type image/svg+xmlAppendix Q: ChangesCheck Update
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SVG 1.1 (Second Edition) – 16 August 2011Top ⋅ Contents ⋅ Previous ⋅ Next ⋅ Elements ⋅ Attributes ⋅ Properties

Appendix F: Implementation Requirements

Contents

  • F.1 Introduction
  • F.2 Error processing
  • F.3 Version control
  • F.4 Clamping values which are restricted to a particular range
  • F.5 ‘path’ element implementation notes
  • F.6 Elliptical arc implementation notes
    • F.6.1 Elliptical arc syntax
    • F.6.2 Out-of-range parameters
    • F.6.3 Parameterization alternatives
    • F.6.4 Conversion from center to endpoint parameterization
    • F.6.5 Conversion from endpoint to center parameterization
    • F.6.6 Correction of out-of-range radii
  • F.7 Text selection implementation notes
  • F.8 Printing implementation notes

This appendix is normative.

F.1 Introduction

The following are notes about implementation requirements corresponding to various features in the SVG language.

F.2 Error processing

There are various scenarios where an SVG document fragment is technically in error:

  • When the content does not conform to the XML 1.0 specification [XML10], such as the use of incorrect XML syntax
  • When an element or attribute is encountered in the document which is not part of the SVG DTD and which is not properly identified as being part of another namespace (see Namespaces in XML [XML-NS])
  • When an element has an attribute or property value which is not permissible according to this specification
  • Other situations that are described as being in error in this specification

A document can go in and out of error over time. For example, document changes from the SVG DOM or from animation can cause a document to become in error and a further change can cause the document to become correct again.

The following error processing shall occur when a document is in error:

  • The document shall be rendered up to, but not including, the first element which has an error. Exceptions:
    • If a ‘path’ element is the first element which has an error and the only errors are in the path data specification, then render the ‘path’ up to the point of the path data error. For related information, see ‘path’ element implementation notes.
    • If a ‘polyline’ or ‘polygon’ element is the first element which has an error and the only errors are within the ‘points’ attribute, then render the ‘polyline’ or ‘polygon’ up to the segment with the error.
    This approach will provide a visual clue to the user or developer about where the error might be in the document.
  • If the document has animations, the animations shall stop at the point at which an error is encountered and the visual presentation of the document shall reflect the animated status of the document at the point the error was encountered.
  • A highly perceivable indication of error shall occur. For visual rendering situations, an example of an indication of error would be to render a translucent colored pattern such as a checkerboard on top of the area where the SVG content is rendered.
  • If the user agent has access to an error reporting capability such as status bar, it is recommended that the user agent provide whatever additional detail it can to enable the user or developer to quickly find the source of the error. For example, the user agent might provide an error message along with a line number and character number at which the error was encountered.

Because of situations where a block of scripting changes might cause a given SVG document fragment to go into and out of error, error processing shall occur only at times when document presentation (e.g., rendering to the display device) is updated. In particular, error processing shall be disabled whenever redraw has been suspended via DOM calls to suspendRedraw.

F.3 Version control

The SVG user agent must verify the reference to the PUBLIC identifier in the <!DOCTYPE> statement or the namespace reference in the ‘xmlns’ attribute on the ‘svg’ element to ensure that the given document (or document fragment) identifies a version of the SVG language which the SVG user agent supports. If the version information is missing or the version information indicates a version of the SVG language which the SVG user agent does not support, then the SVG user agent is not required to render that document or fragment. In particular, it is not required that an SVG user agent attempt to render future versions of the SVG language. If the user environment provides such an option, the user agent should alert or otherwise notify the user that the version of the file is not supported and suggest an alternate processing option (e.g., installing an updated version of the user agent) if such an option exists.

An SVG user agent which supports the SVG Recommendation should alert or otherwise notify the user whenever it encounters an SVG document (or document fragment) whose <!DOCTYPE> statement or corresponding ‘xmlns’ attribute corresponds to a working draft version of the SVG specification. All content based on working drafts of this specification should be updated to the SVG Recommendation.

F.4 Clamping values which are restricted to a particular range

Some numeric attribute and property values have restricted ranges, such as color component values. When out-of-range values are provided, the user agent shall defer any error checking until after presentation time, as composited actions might produce intermediate values which are out-of-range but final values which are within range.

Color values are not in error if they are out-of-range, even if final computations produce an out-of-range color value at presentation time. It is recommended that user agents clamp color values to the nearest color value (possibly determined by simple clipping) which the system can process as late as possible (e.g., presentation time), although it is acceptable for user agents to clamp color values as early as parse time. Thus, implementation dependencies might preclude consistent behavior across different systems when out-of-range color values are used.

Opacity values out-of-range are not in error and should be clamped to the range 0 to 1 at the time which opacity values have to be processed (e.g., at presentation time or when it is necessary to perform intermediate filter effect calculations).

F.5 ‘path’ element implementation notes

A conforming SVG user agent must implement path rendering as follows:

  • Error handling:
    • The general rule for error handling in path data is that the SVG user agent shall render a ‘path’ element up to (but not including) the path command containing the first error in the path data specification. This will provide a visual clue to the user or developer about where the error might be in the path data specification. This rule will greatly discourage generation of invalid SVG path data.
    • If a path data command contains an incorrect set of parameters, then the given path data command is rendered up to and including the last correctly defined path segment, even if that path segment is a sub-component of a compound path data command, such as a "lineto" with several pairs of coordinates. For example, for the path data string 'M 10,10 L 20,20,30', there is an odd number of parameters for the "L" command, which requires an even number of parameters. The user agent is required to draw the line from (10,10) to (20,20) and then perform error reporting since 'L 20 20' is the last correctly defined segment of the path data specification.
    • Wherever possible, all SVG user agents shall report all errors to the user.
  • Markers, directionality and zero-length path segments:
    • If markers are specified, then a marker is drawn on every applicable vertex, even if the given vertex is the end point of a zero-length path segment and even if "moveto" commands follow each other.
    • Certain line-capping and line-joining situations and markers require that a path segment have directionality at its start and end points. Zero-length path segments have no directionality. In these cases, the following algorithm is used to establish directionality: to determine the directionality of the start point of a zero-length path segment, go backwards in the path data specification within the current subpath until you find a segment which has directionality at its end point (e.g., a path segment with non-zero length) and use its ending direction; otherwise, temporarily consider the start point to lack directionality. Similarly, to determine the directionality of the end point of a zero-length path segment, go forwards in the path data specification within the current subpath until you find a segment which has directionality at its start point (e.g., a path segment with non-zero length) and use its starting direction; otherwise, temporarily consider the end point to lack directionality. If the start point has directionality but the end point doesn't, then the end point uses the start point's directionality. If the end point has directionality but the start point doesn't, then the start point uses the end point's directionality. Otherwise, set the directionality for the path segment's start and end points to align with the positive x-axis in user space.
    • As mentioned in Stroke Properties, linecaps must be painted for zero length subpaths when ‘stroke-linecap’ has a value of round or square.
  • The S/s commands indicate that the first control point of the given cubic Bézier segment is calculated by reflecting the previous path segments second control point relative to the current point. The exact math is as follows. If the current point is (curx, cury) and the second control point of the previous path segment is (oldx2, oldy2), then the reflected point (i.e., (newx1, newy1), the first control point of the current path segment) is:
    (newx1, newy1) = (curx - (oldx2 - curx), cury - (oldy2 - cury))
                   = (2*curx - oldx2, 2*cury - oldy2)
    
  • A non-positive radius value is an error.
  • Unrecognized contents within a path data stream (i.e., contents that are not part of the path data grammar) is an error.

F.6 Elliptical arc implementation notes

F.6.1 Elliptical arc syntax

An elliptical arc is a particular path command. As such, it is described by the following parameters in order:

(x1y1) are the absolute coordinates of the current point on the path, obtained from the last two parameters of the previous path command.

rx and ry are the radii of the ellipse (also known as its semi-major and semi-minor axes).

φ is the angle from the x-axis of the current coordinate system to the x-axis of the ellipse.

fA is the large arc flag, and is 0 if an arc spanning less than or equal to 180 degrees is chosen, or 1 if an arc spanning greater than 180 degrees is chosen.

fS is the sweep flag, and is 0 if the line joining center to arc sweeps through decreasing angles, or 1 if it sweeps through increasing angles.

(x2y2) are the absolute coordinates of the final point of the arc.

This parameterization of elliptical arcs will be referred to as endpoint parameterization. One of the advantages of endpoint parameterization is that it permits a consistent path syntax in which all path commands end in the coordinates of the new "current point". The following notes give rules and formulas to help implementers deal with endpoint parameterization.

F.6.2 Out-of-range parameters

Arbitrary numerical values are permitted for all elliptical arc parameters, but where these values are invalid or out-of-range, an implementation must make sense of them as follows:

If the endpoints (x1y1) and (x2y2) are identical, then this is equivalent to omitting the elliptical arc segment entirely.

If rx = 0 or ry = 0 then this arc is treated as a straight line segment (a "lineto") joining the endpoints.

If rx or ry have negative signs, these are dropped; the absolute value is used instead.

If rx, ry and φ are such that there is no solution (basically, the ellipse is not big enough to reach from (x1y1) to (x2y2)) then the ellipse is scaled up uniformly until there is exactly one solution (until the ellipse is just big enough).

φ is taken mod 360 degrees.

Any nonzero value for either of the flags fA or fS is taken to mean the value 1.

This forgiving yet consistent treatment of out-of-range values ensures that:

  • The inevitable approximations arising from computer arithmetic cannot cause a valid set of values written by one SVG implementation to be treated as invalid when read by another SVG implementation. This would otherwise be a problem for common boundary cases such as a semicircular arc.
  • Continuous animations that cause parameters to pass through invalid values are not a problem. The motion remains continuous.

F.6.3 Parameterization alternatives

An arbitrary point (xy) on the elliptical arc can be described by the 2-dimensional matrix equation

equation F.6.3.1 (F.6.3.1)

(cxcy) are the coordinates of the center of the ellipse.

rx and ry are the radii of the ellipse (also known as its semi-major and semi-minor axes).

θ is the angle from the x-axis of the current coordinate system to the x-axis of the ellipse.

θ ranges from:

  • θ1 which is the start angle of the elliptical arc prior to the stretch and rotate operations.
  • θ2 which is the end angle of the elliptical arc prior to the stretch and rotate operations.
  • Δθ which is the difference between these two angles.

If one thinks of an ellipse as a circle that has been stretched and then rotated, then θ1, θ2 and Δθ are the start angle, end angle and sweep angle, respectively of the arc prior to the stretch and rotate operations. This leads to an alternate parameterization which is common among graphics APIs, which will be referred to as center parameterization. In the next sections, formulas are given for mapping in both directions between center parameterization and endpoint parameterization.

F.6.4 Conversion from center to endpoint parameterization

Given the following variables:

cx cy rx ry φ θ1 Δθ

the task is to find:

x1y1x2y2fA fS

This can be achieved using the following formulas:

Equation F.6.4.1 (F.6.4.1)
Equation F.6.4.2 (F.6.4.2)
Equation F.6.4.3 (F.6.4.3)
Equation F.6.4.4 (F.6.4.4)

F.6.5 Conversion from endpoint to center parameterization

Given the following variables:

x1y1x2y2fA fS rx ry φ

the task is to find:

cx cy θ1 Δθ

The equations simplify after a translation which places the origin at the midpoint of the line joining (x1y1) to (x2y2), followed by a rotation to line up the coordinate axes with the axes of the ellipse. All transformed coordinates will be written with primes. They are computed as intermediate values on the way toward finding the required center parameterization variables. This procedure consists of the following steps:

  • Step 1: Compute (x1′, y1′)

    Equation F.6.5.1 (F.6.5.1)
  • Step 2: Compute (cx′, cy′)

    Equation F.6.5.2 (F.6.5.2)

    where the + sign is chosen if fA ≠ fS, and the − sign is chosen if fA = fS.

  • Step 3: Compute (cxcy) from (cx′, cy′)

    Equation F.6.5.3 (F.6.5.3)
  • Step 4: Compute θ1 and Δθ

    In general, the angle between two vectors (uxuy) and (vxvy) can be computed as

    Equation F.6.5.4 (F.6.5.4)

    where the ± sign appearing here is the sign of ux vy − uy vx.

    This angle function can be used to express θ1 and Δθ as follows:

    Equation F.6.5.5 (F.6.5.5)
    Equation F.6.5.6 (F.6.5.6)

    where θ1 is fixed in the range −360° < Δθ < 360° such that:

    if fS = 0, then Δθ < 0,

    else if fS = 1, then Δθ > 0.

    In other words, if fS = 0 and the right side of (F.6.5.6) is greater than 0, then subtract 360°, whereas if fS = 1 and the right side of (F.6.5.6) is less than 0, then add 360°. In all other cases leave it as is.

F.6.6 Correction of out-of-range radii

This section formalizes the adjustments to out-of-range rx and ry mentioned in F.6.2. Algorithmically these adjustments consist of the following steps:

  • Step 1: Ensure radii are non-zero

    If rx = 0 or ry = 0, then treat this as a straight line from (x1y1) to (x2y2) and stop. Otherwise,

  • Step 2: Ensure radii are positive

    Take the absolute value of rx and ry:

    Equation F.6.6.1 (F.6.6.1)
  • Step 3: Ensure radii are large enough

    Using the primed coordinate values of equation (F.6.5.1), compute

    Equation F.6.6.2 (F.6.6.2)

    If the result of the above equation is less than or equal to 1, then no further change need be made to rx and ry. If the result of the above equation is greater than 1, then make the replacements

    Equation F.6.6.3 (F.6.6.3)
  • Step 4: Proceed with computations

    Proceed with the remaining elliptical arc computations, such as those in section F.6.5.  Note: As a consequence of the radii corrections in this section, equation (F.6.5.2) for the center of the ellipse always has at least one solution (i.e. the radicand is never negative).  In the case that the radii are scaled up using equation (F.6.6.3), the radicand of (F.6.5.2) is zero and there is exactly one solution for the center of the ellipse.

F.7 Text selection implementation notes

The following implementation notes describe the algorithm for deciding which characters are selected during a text selection operation.

As the text selection operation occurs (e.g., while the user clicks and drags the mouse to identify the selection), the user agent determines a start selection position and an end selection position, each of which represents a position in the text string between two characters. After determining start selection position and end selection position, the user agent selects the appropriate characters, where the resulting text selection consists of either:

  • no selection or
  • a start character, an end character (possibly the same character), and all of the characters within the same ‘text’ element whose position in the DOM is logically between the start character and end character.

On systems with pointer devices, to determine the start selection position, the SVG user agent determines which boundary between characters corresponding to rendered glyphs is the best target (e.g., closest) based on the current pointer location at the time of the event that initiates the selection operation (e.g., the mouse down event). The user agent then tracks the completion of the selection operation (e.g., the mouse drag, followed ultimately by the mouse up). At the end of the selection operation, the user agent determines which boundary between characters is the best target (e.g., closest) for the end selection position.

If no character reordering has occurred due to bidirectionality, then the selection consists of all characters between the start selection position and end selection position. For example, if a ‘text’ element contains the string "abcdef" and the start selection position and end selection positions are 0 and 3 respectively (assuming the left side of the "a" is position zero), then the selection will consist of "abc".

When the user agent is implementing selection of bidirectional text, and when the selection starts (or ends) between characters which are not contiguous in logical order, then there might be multiple potential combinations of characters that can be considered part of the selection. The algorithms to choose among the combinations of potential selection options shall choose the selection option which most closely matches the text string's visual rendering order.

When multiple characters map inseparably to a given set of one or more glyphs, the user agent can either disallow the selection to start in the middle of the glyph set or can attempt to allocate portions of the area taken up by the glyph set to the characters that correspond to the glyph.

For systems which support pointer devices such as a mouse, the user agent is required to provide a mechanism for selecting text even when the given text has associated event handlers or links, which might block text selection due to event processing precedence rules (see Pointer events). One implementation option: For platforms which support a pointer device such as a mouse, the user agent may provide for a small additional region around character cells which initiates text selection operations but does not initiate event handlers or links.

F.8 Printing implementation notes

For user agents which support both zooming on display devices and printing, it is recommended that the default printing option produce printed output that reflects the display device's current view of the current SVG document fragment (assuming there is no media-specific styling), taking into account any zooming and panning done by the user, the current state of animation, and any document changes due to DOM and scripting. Thus, if the user zooms into a particular area of a map on the display device and then requests a hardcopy, the hardcopy should show the same view of the map as appears on the display device. If a user pauses an animation and prints, the hardcopy should show the same graphics as the currently paused picture on the display device. If scripting has added or removed elements from the document, then the hardcopy should reflect the same changes that would be reflected on the display.

When an SVG document is rendered on a static-only device such as a printer which does not support SVG's animation and scripting and facilities, then the user agent shall ignore any animation and scripting elements in the document and render the remaining graphics elements according to the rules in this specification.

SVG 1.1 (Second Edition) – 16 August 2011Top ⋅ Contents ⋅ Previous ⋅ Next ⋅ Elements ⋅ Attributes ⋅ Properties
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