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04 September 2001

# 1 Introduction

### Contents

## 1.1 About SVG

This specification defines the features and syntax for Scalable Vector Graphics (SVG).

SVG is a language for describing two-dimensional graphics in XML [XML10]. SVG allows for three types of graphic objects: vector graphic shapes (e.g., paths consisting of straight lines and curves), images and text. Graphical objects can be grouped, styled, transformed and composited into previously rendered objects. The feature set includes nested transformations, clipping paths, alpha masks, filter effects and template objects.

SVG drawings can be interactive and dynamic. Animations can be defined and triggered either declaratively (i.e., by embedding SVG animation elements in SVG content) or via scripting.

Sophisticated applications of SVG are possible by use of a supplemental scripting language which accesses SVG Document Object Model (DOM), which provides complete access to all elements, attributes and properties. A rich set of event handlers such as onmouseover and onclick can be assigned to any SVG graphical object. Because of its compatibility and leveraging of other Web standards, features like scripting can be done on XHTML and SVG elements simultaneously within the same Web page.

SVG is a language for rich graphical content. For accessibility reasons, if there is an original source document containing higher-level structure and semantics, it is recommended that the higher-level information be made available somehow, either by making the original source document available, or making an alternative version available in an alternative format which conveys the higher-level information, or by using SVG's facilities to include the higher-level information within the SVG content. For suggested techniques in achieving greater accessibility, see Accessibility.

## 1.2 SVG MIME type, file name extension and Macintosh file type

The MIME type for SVG is "`image/svg+xml`" (see [RFC3023]). The W3C will register this MIME type around the time when SVG is approved as a W3C Recommendation.

It is recommended that SVG files have the extension `".svg"` (all lowercase) on all platforms. It is recommended that gzip-compressed SVG files have the extension `".svgz"` (all lowercase) on all platforms.

It is recommended that SVG files stored on Macintosh HFS file systems be given a file type of `"svg "` (all lowercase, with a space character as the fourth letter). It is recommended that gzip-compressed SVG files stored on Macintosh HFS file systems be given a file type of `"svgz"` (all lowercase).

## 1.3 SVG Namespace, Public Identifier and System Identifier

The following are the SVG 1.0 namespace, public identifier and system identifier:

SVG Namespace:
  http://www.w3.org/2000/svg
Public Identifier for SVG 1.0:
  PUBLIC "-//W3C//DTD SVG 1.0//EN"
System Identifier for SVG 1.0:
  http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd

The following is an example document type declaration for an SVG document:

    <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN"
                  "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">

## 1.4 Compatibility with Other Standards Efforts

SVG leverages and integrates with other W3C specifications and standards efforts. By leveraging and conforming to other standards, SVG becomes more powerful and makes it easier for users to learn how to incorporate SVG into their Web sites.

The following describes some of the ways in which SVG maintains compatibility with, leverages and integrates with other W3C efforts:

- SVG is an application of XML and is compatible with the "Extensible Markup Language (XML) 1.0" Recommendation [XML10]
- SVG is compatible with the "Namespaces in XML" Recommendation [XML-NS]
- SVG utilizes "XML Linking Language (XLink)" [XLINK] for URI referencing and requires support for base URI specifications defined in "XML Base" [XML-BASE].
- SVG's syntax for referencing element IDs is a compatible subset of the ID referencing syntax in "XML Pointer Language (XPointer)" [XPTR].
- SVG content can be styled by either CSS (see "Cascading Style Sheets (CSS) level 2" specification [CSS2]) or XSL (see "XSL Transformations (XSLT) Version 1.0" [XSLT]). (See Styling with CSS and Styling with XSL)
- SVG supports relevant properties and approaches common to CSS and XSL, plus selected semantics and features of CSS (see SVG's styling properties and SVG's Use of Cascading Style Sheets).
- External style sheets are referenced using the mechanism documented in "Associating Style Sheets with XML documents Version 1.0" [XML-SS].
- SVG includes a complete Document Object Model (DOM) and conforms to the "Document Object Model (DOM) level 1" Recommendation [DOM1]. The SVG DOM has a high level of compatibility and consistency with the HTML DOM that is defined in the DOM Level 1 specification. Additionally, the SVG DOM supports and incorporates many of the facilities described in "Document Object Model (DOM) level 2" [DOM2], including the CSS object model and event handling.
- SVG incorporates some features and approaches that are part of the "Synchronized Multimedia Integration Language (SMIL) 1.0 Specification" [SMIL1], including the 'switch' element and the systemLanguage attribute.
- SVG's animation features (see Animation) were developed in collaboration with the W3C Synchronized Multimedia (SYMM) Working Group, developers of the Synchronized Multimedia Integration Language (SMIL) 1.0 Specification [SMIL1]. SVG's animation features incorporate and extend the general-purpose XML animation capabilities described in the "SMIL Animation" specification [SMILANIM].
- SVG has been designed to allow future versions of SMIL to use animated or static SVG content as media components.
- SVG attempts to achieve maximum compatibility with both HTML 4 [HTML4] and XHTML(tm) 1.0 [XHTML]. Many of SVG's facilities are modeled directly after HTML, including its use of CSS [CSS2], its approach to event handling, and its approach to its Document Object Model [DOM2].
- SVG is compatible with W3C work on internationalization. References (W3C and otherwise) include: [UNICODE] and [CHARMOD]. Also, see Internationalization Support.
- SVG is compatible with W3C work on Web Accessibility [WAI]. Also, see Accessibility Support.

In environments which support [DOM2] for other XML grammars (e.g., XHTML [XHTML]) and which also support SVG and the SVG DOM, a single scripting approach can be used simultaneously for both XML documents and SVG graphics, in which case interactive and dynamic effects will be possible on multiple XML namespaces using the same set of scripts.

## 1.5 Terminology

Within this specification, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 (see [RFC2119]). However, for readability, these words do not appear in all uppercase letters in this specification.

At times, this specification recommends good practice for authors and user agents. These recommendations are not normative and conformance with this specification does not depend on their realization. These recommendations contain the expression "We recommend ...", "This specification recommends ...", or some similar wording.

## 1.6 Definitions

basic shape
  Standard shapes which are predefined in SVG as a convenience for common graphical operations. Specifically: 'rect', 'circle', 'ellipse', 'line', 'polyline', 'polygon'.

canvas
  A surface onto which graphics elements are drawn, which can be real physical media such as a display or paper or an abstract surface such as a allocated region of computer memory. See the discussion of the SVG canvas in the chapter on Coordinate Systems, Transformations and Units.

clipping path
  A combination of 'path', 'text' and basic shapes which serve as the outline of a (in the absence of anti-aliasing) 1-bit mask, where everything on the "inside" of the outline is allowed to show through but everything on the outside is masked out. See Clipping paths.

container element
  An element which can have graphics elements and other container elements as child elements. Specifically: 'svg', 'g', 'defs' 'symbol', 'clipPath', 'mask', 'pattern', 'marker', 'a' and 'switch'.

current innermost SVG document fragment
  The XML document sub-tree which starts with the most immediate ancestor 'svg' element of a given SVG element.

current SVG document fragment
  The XML document sub-tree which starts with the outermost ancestor 'svg' element of a given SVG element, with the requirement that all container elements between the outermost 'svg' and this element are all elements in the SVG language.

current transformation matrix (CTM)
  Transformation matrices define the mathematical mapping from one coordinate system into another using a 3x3 matrix using the equation [x' y' 1] = [x y 1] * matrix. The current transformation matrix (CTM) defines the mapping from the user coordinate system into the viewport coordinate system. See Coordinate system transformations.

fill
  The operation of painting the interior of a shape or the interior of the character glyphs in a text string.

font
  A font represents an organized collection of glyphs in which the various glyph representations will share a common look or styling such that, when a string of characters is rendered together, the result is highly legible, conveys a particular artistic style and provides consistent inter-character alignment and spacing.

glyph
  A glyph represents a unit of rendered content within a font. Often, there is a one-to-one correspondence between characters to be drawn and corresponding glyphs (e.g., often, the character "A" is rendered using a single glyph), but other times multiple glyphs are used to render a single character (e.g., use of accents) or a single glyph can be used to render multiple characters (e.g., ligatures). Typically, a glyph is defined by one or more shapes such as a path, possibly with additional information such as rendering hints that help a font engine to produce legible text in small sizes.

graphics element
  One of the element types that can cause graphics to be drawn onto the target canvas. Specifically: 'path', 'text', 'rect', 'circle', 'ellipse', 'line', 'polyline', 'polygon', 'image' and 'use'.

graphics referencing element
  A graphics element which uses a reference to a different document or element as the source of its graphical content. Specifically: 'use' and 'image'.

local URI reference
  A Uniform Resource Identifier [URI] that does not include an <absoluteURI> or <relativeURI> and thus represents a reference to an element within the current document. See References and the 'defs' element.

mask
  A container element which can contain graphics elements or other container elements which define a set of graphics that is to be used as a semi-transparent mask for compositing foreground objects into the current background. See Masks.

non-local URI reference
  A Uniform Resource Identifier [URI] that includes an <absoluteURI> or <relativeURI> and thus (usually) represents a reference to a different document or an element within a different document. See References and the 'defs' element.

paint
  A paint represents a way of putting color values onto the canvas. A paint might consist of both color values and associated alpha values which control the blending of colors against already existing color values on the canvas. SVG supports three types of built-in paint: color, gradients and patterns.

presentation attribute
  An XML attribute on an SVG element which specifies a value for a given property for that element. See Styling.

property
  A parameter that helps specify how a document should be rendered. A complete list of SVG's properties can be found in Property Index. Properties are assigned to elements in the SVG language either by presentation attributes on elements in the SVG language or by using a styling language such as CSS [CSS2]. See Styling.

shape
  A graphics element that is defined by some combination of straight lines and curves. Specifically: 'path', 'rect', 'circle', 'ellipse', 'line', 'polyline', 'polygon'.

stroke
  The operation of painting the outline of a shape or the outline of character glyphs in a text string.

SVG canvas
  The canvas onto which the SVG content is rendered. See the discussion of the SVG canvas in the chapter on Coordinate Systems, Transformations and Units.

SVG document fragment
  The XML document sub-tree which starts with an 'svg' element. An SVG document fragment can consist of a stand-alone SVG document, or a fragment of a parent XML document enclosed by an 'svg' element. When an 'svg' element is a descendant of another 'svg' element, there are two SVG document fragments, one for each 'svg' element. (One SVG document fragment is contained within another SVG document fragment.)

SVG viewport
  The viewport within the SVG canvas which defines the rectangular region into which SVG content is rendered. See the discussion of the SVG viewport in the chapter on Coordinate Systems, Transformations and Units.

text content element
  One of SVG's elements that can define a text string that is to be rendered onto the canvas. SVG's text content elements are the following: 'text', 'tspan', 'tref', 'textPath' and 'altGlyph'.

transformation
  A modification of the current transformation matrix (CTM) by providing a supplemental transformation in the form of a set of simple transformations specifications (such as scaling, rotation or translation) and/or one or more transformation matrices. See Coordinate system transformations.

transformation matrix
  Transformation matrices define the mathematical mapping from one coordinate system into another using a 3x3 matrix using the equation [x' y' 1] = [x y 1] * matrix. See current transformation matrix (CTM) and Coordinate system transformations.

URI Reference
  A Uniform Resource Identifier [URI] which serves as a reference to a file or to an element within a file. See References and the 'defs' element.

user agent
  The general definition of a user agent is an application that retrieves and renders Web content, including text, graphics, sounds, video, images, and other content types. A user agent may require additional user agents that handle some types of content. For instance, a browser may run a separate program or plug-in to render sound or video. User agents include graphical desktop browsers, multimedia players, text browsers, voice browsers, and assistive technologies such as screen readers, screen magnifiers, speech synthesizers, onscreen keyboards, and voice input software.
  A "user agent" may or may not have the ability to retrieve and render SVG content; however, an "SVG user agent" retrieves and renders SVG content.

user coordinate system
  In general, a coordinate system defines locations and distances on the current canvas. The current user coordinate system is the coordinate system that is currently active and which is used to define how coordinates and lengths are located and computed, respectively, on the current canvas. See initial user coordinate system and Coordinate system transformations.

user space
  A synonym for user coordinate system.

user units
  A coordinate value or length expressed in user units represents a coordinate value or length in the current user coordinate system. Thus, 10 user units represents a length of 10 units in the current user coordinate system.

viewport
  A rectangular region within the current canvas onto which graphics elements are to be rendered. See the discussion of the SVG viewport in the chapter on Coordinate Systems, Transformations and Units.

viewport coordinate system
  In general, a coordinate system defines locations and distances on the current canvas. The viewport coordinate system is the coordinate system that is active at the start of processing of an 'svg' element, before processing the optional viewBox attribute. In the case of an SVG document fragment that is embedded within a parent document which uses CSS to manage its layout, then the viewport coordinate system will have the same orientation and lengths as in CSS, with the origin at the top-left on the viewport. See The initial viewport and Establishing a new viewport.

viewport space
  A synonym for viewport coordinate system.

viewport units
  A coordinate value or length expressed in viewport units represents a coordinate value or length in the viewport coordinate system. Thus, 10 viewport units represents a length of 10 units in the viewport coordinate system.

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