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Scalable Vector Graphics (SVG) 1.1 (Second Edition) 1 Introduction 1.1 About SVG 1.2 SVG MIME type 1.3 SVG Namespace 1.4 Compatibility with Other Standards Efforts 1.5 Terminology 1.6 Definitions 2 Concepts 2.1 Explaining the name: SVG 2.2 Important SVG concepts 2.3 Options for using SVG in Web pages 3 Rendering Model 3.1 Introduction 3.2 The painters model 3.3 Rendering Order 3.4 How groups are rendered 3.5 How elements are rendered 3.6 Types of graphics elements 3.6.1 Painting shapes and text 3.6.2 Painting raster images 3.7 Filtering painted regions 3.8 Clipping 3.9 Parent Compositing 4 Basic Data Types and Interfaces 4.1 Syntax 4.2 Basic data types 4.3 Real number precision 4.4 Recognized color keyword names 4.5 Basic DOM interfaces 4.5.1 Interface SVGElement 4.5.2 Interface SVGAnimatedBoolean 4.5.3 Interface SVGAnimatedString 4.5.4 Interface SVGStringList 4.5.5 Interface SVGAnimatedEnumeration 4.5.6 Interface SVGAnimatedInteger 4.5.7 Interface SVGNumber 4.5.8 Interface SVGAnimatedNumber 4.5.9 Interface SVGNumberList 4.5.10 Interface SVGAnimatedNumberList 4.5.11 Interface SVGLength 4.5.12 Interface SVGAnimatedLength 4.5.13 Interface SVGLengthList 4.5.14 Interface SVGAnimatedLengthList 4.5.15 Interface SVGAngle 4.5.16 Interface SVGAnimatedAngle 4.5.17 Interface SVGColor 4.5.18 Interface SVGICCColor 4.5.19 Interface SVGRect 4.5.20 Interface SVGAnimatedRect 4.5.21 Interface SVGUnitTypes 4.5.22 Interface SVGStylable 4.5.23 Interface SVGLocatable 4.5.24 Interface SVGTransformable 4.5.25 Interface SVGTests 4.5.26 Interface SVGLangSpace 4.5.27 Interface SVGExternalResourcesRequired 4.5.28 Interface SVGFitToViewBox 4.5.29 Interface SVGZoomAndPan 4.5.30 Interface SVGViewSpec 4.5.31 Interface SVGURIReference 4.5.32 Interface SVGCSSRule 4.5.33 Interface SVGRenderingIntent 5 Document Structure 5.1 Defining an SVG document fragment: the 憇vg?element 5.1.1 Overview 5.1.2 The 憇vg?element 5.2 Grouping: the 慻?element 5.2.1 Overview 5.2.2 The 慻?element 5.3 Defining content for reuse 5.3.1 Overview 5.3.2 The 慸efs?element 5.4 The 慸esc?and 憈itle?elements 5.5 The 憇ymbol?element 5.6 The 憉se?element 5.7 The 慽mage?element 5.8 Conditional processing 5.8.1 Conditional processing overview 5.8.2 The 憇witch?element 5.8.3 The 憆equiredFeatures?attribute 5.8.4 The 憆equiredExtensions?attribute 5.8.5 The 憇ystemLanguage?attribute 5.8.6 Applicability of test attributes 5.9 Specifying whether external resources are required for proper rendering 5.10 Common attributes 5.10.1 Attributes common to all elements: 慽d?and 憍ml:base? 5.10.2 The 憍ml:lang?and 憍ml:space?attributes 5.11 DOM interfaces 5.11.1 Interface SVGDocument 5.11.2 Interface SVGSVGElement 5.11.3 Interface SVGGElement 5.11.4 Interface SVGDefsElement 5.11.5 Interface SVGDescElement 5.11.6 Interface SVGTitleElement 5.11.7 Interface SVGSymbolElement 5.11.8 Interface SVGUseElement 5.11.9 Interface SVGElementInstance 5.11.10 Interface SVGElementInstanceList 5.11.11 Interface SVGImageElement 5.11.12 Interface SVGSwitchElement 5.11.13 Interface GetSVGDocument 6 Styling 6.1 SVG's styling properties 6.2 Usage scenarios for styling 6.3 Alternative ways to specify styling properties 6.4 Specifying properties using the presentation attributes 6.5 Styling with XSL 6.6 Styling with CSS 6.7 Case sensitivity of property names and values 6.8 Facilities from CSS and XSL used by SVG 6.9 Referencing external style sheets 6.10 The 憇tyle?element 6.11 The 慶lass?attribute 6.12 The 憇tyle?attribute 6.13 Specifying the default style sheet language 6.14 Property inheritance 6.15 The scope/range of styles 6.16 User agent style sheet 6.17 Aural style sheets 6.18 DOM interfaces 6.18.1 Interface SVGStyleElement 7 Coordinate Systems 7.1 Introduction 7.2 The initial viewport 7.3 The initial coordinate system 7.4 Coordinate system transformations 7.5 Nested transformations 7.6 The 憈ransform?attribute 7.7 The 憊iewBox?attribute 7.8 The 憄reserveAspectRatio?attribute 7.9 Establishing a new viewport 7.10 Units 7.11 Object bounding box units 7.12 Intrinsic sizing properties of the viewport of SVG content 7.13 Geographic coordinate systems 7.14 The 憇vg:transform?attribute 7.15 DOM interfaces 7.15.1 Interface SVGPoint 7.15.2 Interface SVGPointList 7.15.3 Interface SVGMatrix 7.15.4 Interface SVGTransform 7.15.5 Interface SVGTransformList 7.15.6 Interface SVGAnimatedTransformList 7.15.7 Interface SVGPreserveAspectRatio 7.15.8 Interface SVGAnimatedPreserveAspectRatio 8 Paths 8.1 Introduction 8.2 The 憄ath?element 8.3 Path data 8.3.1 General information about path data 8.3.2 The "moveto" commands 8.3.3 The "closepath" command 8.3.4 The "lineto" commands 8.3.5 The curve commands 8.3.6 The cubic B閦ier curve commands 8.3.7 The quadratic B閦ier curve commands 8.3.8 The elliptical arc curve commands 8.3.9 The grammar for path data 8.4 Distance along a path 8.5 DOM interfaces 8.5.1 Interface SVGPathSeg 8.5.2 Interface SVGPathSegClosePath 8.5.3 Interface SVGPathSegMovetoAbs 8.5.4 Interface SVGPathSegMovetoRel 8.5.5 Interface SVGPathSegLinetoAbs 8.5.6 Interface SVGPathSegLinetoRel 8.5.7 Interface SVGPathSegCurvetoCubicAbs 8.5.8 Interface SVGPathSegCurvetoCubicRel 8.5.9 Interface SVGPathSegCurvetoQuadraticAbs 8.5.10 Interface SVGPathSegCurvetoQuadraticRel 8.5.11 Interface SVGPathSegArcAbs 8.5.12 Interface SVGPathSegArcRel 8.5.13 Interface SVGPathSegLinetoHorizontalAbs 8.5.14 Interface SVGPathSegLinetoHorizontalRel 8.5.15 Interface SVGPathSegLinetoVerticalAbs 8.5.16 Interface SVGPathSegLinetoVerticalRel 8.5.17 Interface SVGPathSegCurvetoCubicSmoothAbs 8.5.18 Interface SVGPathSegCurvetoCubicSmoothRel 8.5.19 Interface SVGPathSegCurvetoQuadraticSmoothAbs 8.5.20 Interface SVGPathSegCurvetoQuadraticSmoothRel 8.5.21 Interface SVGPathSegList 8.5.22 Interface SVGAnimatedPathData 8.5.23 Interface SVGPathElement 9 Basic Shapes 9.1 Introduction 9.2 The 憆ect?element 9.3 The 慶ircle?element 9.4 The 慹llipse?element 9.5 The 憀ine?element 9.6 The 憄olyline?element 9.7 The 憄olygon?element 9.7.1 The grammar for points specifications in 憄olyline?and 憄olygon?elements 9.8 DOM interfaces 9.8.1 Interface SVGRectElement 9.8.2 Interface SVGCircleElement 9.8.3 Interface SVGEllipseElement 9.8.4 Interface SVGLineElement 9.8.5 Interface SVGAnimatedPoints 9.8.6 Interface SVGPolylineElement 9.8.7 Interface SVGPolygonElement 10 Text 10.1 Introduction 10.2 Characters and their corresponding glyphs 10.3 Fonts 10.4 The 憈ext?element 10.5 The 憈span?element 10.6 The 憈ref?element 10.7 Text layout 10.7.1 Text layout introduction 10.7.2 Setting the inline-progression-direction 10.7.3 Glyph orientation within a text run 10.7.4 Relationship with bidirectionality 10.8 Text rendering order 10.9 Alignment properties 10.9.1 Text alignment properties 10.9.2 Baseline alignment properties 10.10 Font selection properties 10.11 Spacing properties 10.12 Text decoration 10.13 Text on a path 10.13.1 Introduction to text on a path 10.13.2 The 憈extPath?element 10.13.3 Text on a path layout rules 10.14 Alternate glyphs 10.14.1 The 慳ltGlyph?element 10.14.2 The 慳ltGlyphDef? 慳ltGlyphItem?and 慻lyphRef?elements 10.15 White space handling 10.16 Text selection and clipboard operations 10.17 DOM interfaces 10.17.1 Interface SVGTextContentElement 10.17.2 Interface SVGTextPositioningElement 10.17.3 Interface SVGTextElement 10.17.4 Interface SVGTSpanElement 10.17.5 Interface SVGTRefElement 10.17.6 Interface SVGTextPathElement 10.17.7 Interface SVGAltGlyphElement 10.17.8 Interface SVGAltGlyphDefElement 10.17.9 Interface SVGAltGlyphItemElement 10.17.10 Interface SVGGlyphRefElement 11 Painting: Filling 11.1 Introduction 11.2 Specifying paint 11.3 Fill Properties 11.4 Stroke Properties 11.5 Controlling visibility 11.6 Markers 11.6.1 Introduction 11.6.2 The 憁arker?element 11.6.3 Marker properties 11.6.4 Details on how markers are rendered 11.7 Rendering properties 11.7.1 Color interpolation properties: 慶olor-interpolation?and 慶olor-interpolation-filters? 11.7.2 The 慶olor-rendering?property 11.7.3 The 憇hape-rendering?property 11.7.4 The 憈ext-rendering?property 11.7.5 The 慽mage-rendering?property 11.8 Inheritance of painting properties 11.9 DOM interfaces 11.9.1 Interface SVGPaint 11.9.2 Interface SVGMarkerElement 12 Color 12.1 Introduction 12.2 The 慶olor?property 12.3 Color profile descriptions 12.3.1 Overview of color profile descriptions 12.3.2 Alternative ways of defining a color profile description 12.3.3 The 慶olor-profile?element 12.3.4 The CSS @color-profile rule 12.3.5 The 慶olor-profile?property 12.4 DOM interfaces 12.4.1 Interface SVGColorProfileElement 12.4.2 Interface SVGColorProfileRule 13 Gradients and Patterns 13.1 Introduction 13.2 Gradients 13.2.1 Introduction 13.2.2 Linear gradients 13.2.3 Radial gradients 13.2.4 Gradient stops 13.3 Patterns 13.4 DOM interfaces 13.4.1 Interface SVGGradientElement 13.4.2 Interface SVGLinearGradientElement 13.4.3 Interface SVGRadialGradientElement 13.4.4 Interface SVGStopElement 13.4.5 Interface SVGPatternElement 14 Clipping 14.1 Introduction 14.2 Simple alpha compositing 14.3 Clipping paths 14.3.1 Introduction 14.3.2 The initial clipping path 14.3.3 The 憃verflow?and 慶lip?properties 14.3.4 Clip to viewport vs. clip to 憊iewBox? 14.3.5 Establishing a new clipping path: the 慶lipPath?element 14.3.6 Clipping paths 14.4 Masking 14.5 Object and group opacity: the 憃pacity?property 14.6 DOM interfaces 14.6.1 Interface SVGClipPathElement 14.6.2 Interface SVGMaskElement 15 Filter Effects 15.1 Introduction 15.2 An example 15.3 The 慺ilter?element 15.4 The 慺ilter?property 15.5 Filter effects region 15.6 Accessing the background image 15.7 Filter primitives overview 15.7.1 Overview 15.7.2 Common attributes 15.7.3 Filter primitive subregion 15.8 Light source elements and properties 15.8.1 Introduction 15.8.2 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?property 15.9 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 interfaces 15.25.1 Interface SVGFilterElement 15.25.2 Interface SVGFilterPrimitiveStandardAttributes 15.25.3 Interface SVGFEBlendElement 15.25.4 Interface SVGFEColorMatrixElement 15.25.5 Interface SVGFEComponentTransferElement 15.25.6 Interface SVGComponentTransferFunctionElement 15.25.7 Interface SVGFEFuncRElement 15.25.8 Interface SVGFEFuncGElement 15.25.9 Interface SVGFEFuncBElement 15.25.10 Interface SVGFEFuncAElement 15.25.11 Interface SVGFECompositeElement 15.25.12 Interface SVGFEConvolveMatrixElement 15.25.13 Interface SVGFEDiffuseLightingElement 15.25.14 Interface SVGFEDistantLightElement 15.25.15 Interface SVGFEPointLightElement 15.25.16 Interface SVGFESpotLightElement 15.25.17 Interface SVGFEDisplacementMapElement 15.25.18 Interface SVGFEFloodElement 15.25.19 Interface SVGFEGaussianBlurElement 15.25.20 Interface SVGFEImageElement 15.25.21 Interface SVGFEMergeElement 15.25.22 Interface SVGFEMergeNodeElement 15.25.23 Interface SVGFEMorphologyElement 15.25.24 Interface SVGFEOffsetElement 15.25.25 Interface SVGFESpecularLightingElement 15.25.26 Interface SVGFETileElement 15.25.27 Interface SVGFETurbulenceElement 16 Interactivity 16.1 Introduction 16.2 Complete list of supported events 16.3 User interface events 16.4 Pointer events 16.5 Hit-testing and processing order for user interface events 16.5.1 Hit-testing 16.5.2 Event processing 16.6 The 憄ointer-events?property 16.7 Magnification and panning 16.8 Cursors 16.8.1 Introduction to cursors 16.8.2 The 慶ursor?property 16.8.3 The 慶ursor?element 16.9 DOM interfaces 16.9.1 Interface SVGCursorElement 17 Linking 17.1 References 17.1.1 Overview 17.1.2 IRIs and URIs 17.1.3 Syntactic forms: IRI and FuncIRI 17.1.4 Processing of IRI references 17.1.5 IRI reference attributes 17.2 Links out of SVG content: the 慳?element 17.3 Linking into SVG content: IRI fragments and SVG views 17.3.1 Introduction: IRI fragments and SVG views 17.3.2 SVG fragment identifiers 17.3.3 Predefined views: the 憊iew?element 17.3.4 Highlighting views 17.4 DOM interfaces 17.4.1 Interface SVGAElement 17.4.2 Interface SVGViewElement 18 Scripting 18.1 Specifying the scripting language 18.1.1 Specifying the default scripting language 18.1.2 Local declaration of a scripting language 18.2 The 憇cript?element 18.3 Event handling 18.4 Event attributes 18.4.1 Event attribute for the SVGLoad event 18.4.2 Event attributes on graphics and container elements 18.4.3 Document-level event attributes 18.4.4 Animation event attributes 18.5 DOM interfaces 18.5.1 Interface SVGScriptElement 18.5.2 Interface SVGZoomEvent 19 Animation 19.1 Introduction 19.2 Animation elements 19.2.1 Overview 19.2.2 Relationship to SMIL Animation 19.2.3 Animation elements example 19.2.4 Attributes to identify the target element for an animation 19.2.5 Attributes to identify the target attribute or property for an animation 19.2.6 Animation with namespaces 19.2.7 Paced animation and complex types 19.2.8 Attributes to control the timing of the animation 19.2.8.1 Clock values 19.2.9 Attributes that define animation values over time 19.2.10 Attributes that control whether animations are additive 19.2.11 Inheritance 19.2.12 The 慳nimate?element 19.2.13 The 憇et?element 19.2.14 The 慳nimateMotion?element 19.2.15 The 慳nimateColor?element 19.2.16 The 慳nimateTransform?element 19.2.17 Elements 19.3 Animation using the SVG DOM 19.4 DOM interfaces 19.4.1 Interface ElementTimeControl 19.4.2 Interface TimeEvent 19.4.3 Interface SVGAnimationElement 19.4.4 Interface SVGAnimateElement 19.4.5 Interface SVGSetElement 19.4.6 Interface SVGAnimateMotionElement 19.4.7 Interface SVGMPathElement 19.4.8 Interface SVGAnimateColorElement 19.4.9 Interface SVGAnimateTransformElement 20 Fonts 20.1 Introduction 20.2 Overview of SVG fonts 20.3 The 慺ont?element 20.4 The 慻lyph?element 20.5 The 憁issing-glyph?element 20.6 Glyph selection rules 20.7 The 慼kern?and 憊kern?elements 20.8 Describing a font 20.8.1 Overview of font descriptions 20.8.2 Alternative ways for providing a font description 20.8.3 The 慺ont-face?element 20.8.4 The 慺ont-face-src?element 20.8.5 The 慺ont-face-uri?and 慺ont-face-format?elements 20.8.6 The 慺ont-face-name?element 20.9 DOM interfaces 20.9.1 Interface SVGFontElement 20.9.2 Interface SVGGlyphElement 20.9.3 Interface SVGMissingGlyphElement 20.9.4 Interface SVGHKernElement 20.9.5 Interface SVGVKernElement 20.9.6 Interface SVGFontFaceElement 20.9.7 Interface SVGFontFaceSrcElement 20.9.8 Interface SVGFontFaceUriElement 20.9.9 Interface SVGFontFaceFormatElement 20.9.10 Interface SVGFontFaceNameElement 21 Metadata 21.1 Introduction 21.2 The 憁etadata?element 21.3 An example 21.4 DOM interfaces 21.4.1 Interface SVGMetadataElement 22 Backwards Compatibility 23 Extensibility 23.1 Foreign namespaces and private data 23.2 Embedding foreign object types 23.3 The 慺oreignObject?element 23.4 An example 23.5 Adding private elements and attributes to the DTD 23.6 DOM interfaces 23.6.1 Interface SVGForeignObjectElement Appendix A: Document Type Definition A.1 Introduction A.2 Modularization A.2.1 Element and attribute collections A.2.2 Profiling the SVG specification A.2.3 Practical considerations A.3 SVG 1.1 module definitions and DTD implementations A.3.1 Modular Framework Module A.3.2 Datatypes Module A.3.3 Qualified Name Module A.3.4 Core Attribute Module A.3.5 Container Attribute Module A.3.6 Viewport Attribute Module A.3.7 Paint Attribute Module A.3.8 Basic Paint Attribute Module A.3.9 Paint Opacity Attribute Module A.3.10 Graphics Attribute Module A.3.11 Basic Graphics Attribute Module A.3.12 Document Events Attribute Module A.3.13 Graphical Element Events Attribute Module A.3.14 Animation Events Attribute Module A.3.15 XLink Attribute Module A.3.16 External Resources Attribute Module A.3.17 Structure Module A.3.18 Basic Structure Module A.3.19 Conditional Processing Module A.3.20 Image Module A.3.21 Style Module A.3.22 Shape Module A.3.23 Text Module A.3.24 Basic Text Module A.3.25 Marker Module A.3.26 Color Profile Module A.3.27 Gradient Module A.3.28 Pattern Module A.3.29 Clip Module A.3.30 Basic Clip Module A.3.31 Mask Module A.3.32 Filter Module A.3.33 Basic Filter Module A.3.34 Cursor Module A.3.35 Hyperlinking Module A.3.36 View Module A.3.37 Scripting Module A.3.38 Animation Module A.3.39 Font Module A.3.40 Basic Font Module A.3.41 Extensibility Module A.4 SVG 1.1 Document Type Definition A.4.1 SVG 1.1 DTD Driver A.4.2 SVG 1.1 Document Model A.4.3 SVG 1.1 Attribute Collection Appendix B: SVG Document Object Model (DOM) B.1 SVG DOM overview B.1.1 SVG DOM object initialization B.2 Elements in the SVG DOM B.3 Naming conventions B.4 Exception SVGException B.5 Feature strings for the hasFeature method call B.6 Relationship with DOM Level 2 Events B.7 Relationship with DOM Level 2 CSS B.7.1 Introduction B.7.2 User agents that do not support styling with CSS B.7.3 User agents that support styling with CSS B.7.4 Extended interfaces B.8 Read only nodes in the DOM B.9 Invalid values Appendix C: IDL Definitions Appendix D: Java Language Binding D.1 The Java language binding D.2 Using SVG with the Java language Appendix E: ECMAScript Language Binding E.1 Exceptions E.2 Constants E.3 Types E.4 Objects Appendix F: Implementation Requirements F.1 Introduction F.2 Error processing F.3 Version control F.4 Clamping values which are restricted to a particular range F.5 憄ath?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 Appendix G: Conformance Criteria G.1 Introduction G.2 Conforming SVG Document Fragments G.3 Conforming SVG Stand-Alone Files G.4 Conforming SVG Generators G.5 Conforming SVG Servers G.6 Conforming SVG DOM Subtree G.7 Conforming SVG Interpreters G.8 Conforming SVG Viewers Appendix H: Accessibility Support H.1 WAI Accessibility Guidelines H.2 SVG Content Accessibility Guidelines Appendix I: Internationalization Support I.1 Introduction I.2 Internationalization and SVG I.3 SVG Internationalization Guidelines Appendix J: Minimizing SVG File Sizes Appendix K: References K.1 Normative references K.2 Informative references Appendix L: Element Index Appendix M: Attribute Index M.1 Regular attributes M.2 Presentation attributes Appendix N: Property Index Appendix O: Feature Strings O.1 Introduction O.2 SVG 1.1 feature strings O.3 SVG 1.0 feature strings Appendix P: Media Type Registration for image/svg+xml P.1 Introduction P.2 Registration of media type image/svg+xml Appendix Q: Changes Check Update

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2 Concepts

2.1 Explaining the name: SVG
2.2 Important SVG concepts
2.3 Options for using SVG in Web pages

2.1 Explaining the name: SVG

SVG stands for Scalable Vector Graphics, an XML grammar for stylable graphics, usable as an XML namespace.

Scalable

To be scalable means to increase or decrease uniformly. In terms of graphics, scalable means not being limited to a single, fixed, pixel size. On the Web, scalable means that a particular technology can grow to a large number of files, a large number of users, a wide variety of applications. SVG, being a graphics technology for the Web, is scalable in both senses of the word.

SVG graphics are scalable to different display resolutions, so that for example printed output uses the full resolution of the printer and can be displayed at the same size on screens of different resolutions. The same SVG graphic can be placed at different sizes on the same Web page, and re-used at different sizes on different pages. SVG graphics can be magnified to see fine detail, or to aid those with low vision.

SVG graphics are scalable because the same SVG content can be a stand-alone graphic or can be referenced or included inside other SVG graphics, thereby allowing a complex illustration to be built up in parts, perhaps by several people. The symbol, marker and font capabilities promote re-use of graphical components, maximize the advantages of HTTP caching and avoid the need for a centralized registry of approved symbols.

Vector

Vector graphics contain geometric objects such as lines and curves. This gives greater flexibility compared to raster-only formats (such as PNG and JPEG) which have to store information for every pixel of the graphic. Typically, vector formats can also integrate raster images and can combine them with vector information such as clipping paths to produce a complete illustration; SVG is no exception.

Since all modern displays are raster-oriented, the difference between raster-only and vector graphics comes down to where they are rasterized; client side in the case of vector graphics, as opposed to already rasterized on the server. SVG gives control over the rasterization process, for example to allow anti-aliased artwork without the ugly aliasing typical of low quality vector implementations. SVG also provides client-side raster filter effects, so that moving to a vector format does not mean the loss of popular effects such as soft drop shadows.

Graphics

Most existing XML grammars represent either textual information, or represent raw data such as financial information. They typically provide only rudimentary graphical capabilities, often less capable than the HTML 'img' element. SVG fills a gap in the market by providing a rich, structured description of vector and mixed vector/raster graphics; it can be used stand-alone, or as an XML namespace with other grammars.

XML

XML, a for structured information exchange, has become extremely popular and is both widely and reliably implemented. By being written in XML, SVG builds on this strong foundation and gains many advantages such as a sound basis for internationalization, powerful structuring capability, an object model, and so on. By building on existing, cleanly-implemented specifications, XML-based grammars are open to implementation without a huge reverse engineering effort.

Namespace

It is certainly useful to have a stand-alone, SVG-only viewer. But SVG is also intended to be used as one component in a multi-namespace XML application. This multiplies the power of each of the namespaces used, to allow innovative new content to be created. For example, SVG graphics may be included in a document which uses any text-oriented XML namespace - including XHTML. A scientific document, for example, might also use MathML for mathematics in the document. The combination of SVG and SMIL leads to interesting, time based, graphically rich presentations.

SVG is a good, general-purpose component for any multi-namespace grammar that needs to use graphics.

Stylable

The advantages of style sheets in terms of presentational control, flexibility, faster download and improved maintenance are now generally accepted, certainly for use with text. SVG extends this control to the realm of graphics.

The combination of scripting, DOM and CSS is often termed "Dynamic HTML" and is widely used for animation, interactivity and presentational effects. SVG allows the same script-based manipulation of the document tree and the style sheet.

2.2 Important SVG concepts

Graphical Objects

With any XML grammar, consideration has to be given to what exactly is being modelled. For textual formats, modelling is typically at the level of paragraphs and phrases, rather than individual nouns, adverbs, or phonemes. Similarly, SVG models graphics at the level of graphical objects rather than individual points.

SVG provides a general path element, which can be used to create a huge variety of graphical objects, and also provides common basic shapes such as rectangles and ellipses. These are convenient for hand coding and may be used in the same ways as the more general path element. SVG provides fine control over the coordinate system in which graphical objects are defined and the transformations that will be applied during rendering.

Symbols

It would have been possible to define some standard symbols that SVG would provide. But which ones? There would always be additional symbols for electronics, cartography, flowcharts, etc., that people would need that were not provided until the "next version". SVG allows users to create, re-use and share their own symbols without requiring a centralized registry. Communities of users can create and refine the symbols that they need, without having to ask a committee. Designers can be sure exactly of the graphical appearance of the symbols they use and not have to worry about unsupported symbols.

Symbols may be used at different sizes and orientations, and can be restyled to fit in with the rest of the graphical composition.

Raster Effects

Many existing Web graphics use the filtering operations found in paint packages to create blurs, shadows, lighting effects and so on. With the client-side rasterization used with vector formats, such effects might be thought impossible. SVG allows the declarative specification of filters, either singly or in combination, which can be applied on the client side when the SVG is rendered. These are specified in such a way that the graphics are still scalable and displayable at different resolutions.

Fonts

Graphically rich material is often highly dependent on the particular font used and the exact spacing of the glyphs. In many cases, designers convert text to outlines to avoid any font substitution problems. This means that the original text is not present and thus searchability and accessibility suffer. In response to feedback from designers, SVG includes font elements so that both text and graphical appearance are preserved.

Animation

Animation can be produced via script-based manipulation of the document, but scripts are difficult to edit and interchange between authoring tools is harder. Again in response to feedback from the design community, SVG includes declarative animation elements which were designed collaboratively by the SVG and SYMM Working Groups. This allows the animated effects common in existing Web graphics to be expressed in SVG.

2.3 Options for using SVG in Web pages

There are a variety of ways in which SVG content can be included within a Web page. Here are some of the options:

A stand-alone SVG Web page

In this case, an SVG document (i.e., a Web resource whose MIME type is "image/svg+xml") is loaded directly into a user agent such as a Web browser. The SVG document is the Web page that is presented to the user.

Embedding by reference

In this case, a parent Web page references a separately stored SVG document and specifies that the given SVG document should be embedded as a component of the parent Web page. For HTML or XHTML, here are three options:

The HTML/XHTML ‘img’ element is the most common method for using graphics in HTML pages. For faster display, the width and height of the image can be given as attributes. One attribute that is required is ‘alt’, used to give an alternate textual string for people browsing with images off, or who cannot see the images. The string cannot contain any markup. A ‘longdesc’ attribute lets you point to a longer description - often in HTML - which can have markup and richer formatting.
The HTML/XHTML ‘object’ element can contain other elements nested within it, unlike ‘img’, which is empty. This means that several different formats can be offered, using nested ‘object’ elements, with a final textual alternative (including markup, links, etc). The outermost element which can be displayed will be used.
The HTML/XHTML ‘applet’ element which can invoke a Java applet to view SVG content within the given Web page. These applets can do many things, but a common task is to use them to display images, particularly ones in unusual formats or which need to be presented under the control of a program for some other reason.

Embedding inline

In this case, SVG content is embedded inline directly within the parent Web page. An example is an XHTML Web page with an SVG document fragment textually included within the XHTML.

External link, using the HTML ‘a’ element

This allows any stand-alone SVG viewer to be used, which can (but need not) be a different program to that used to display HTML. This option typically is used for unusual image formats.

Referenced from a CSS or XSL property

When a user agent supports CSS-styled XML content [CSS2] or XSL [XSL] and the user agent is a Conforming SVG Viewer, then that user agent must support the ability to reference SVG resources wherever CSS or XSL properties allow for the referencing of raster images, including the ability to tile SVG graphics wherever necessary and the ability to composite the SVG into the background if it has transparent portions. Examples include the ‘background-image’ and ‘list-style-image’ properties ([CSS2], sections 14.2.1 and 12.6.2) that are included in both CSS and XSL.

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