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.
SVG 1.1 is a modularization of SVG 1.0 [SVG10].
See the Document Type Definition appendix for
details on how the DTD is structured to allow profiling and composition with
other XML languages.
1.2 SVG MIME type, file name extension and Macintosh file
type
The MIME type for SVG is "image/svg+xml" (see
XML Media Types
[RFC3023]). The
registration of this MIME type is in progress at the W3C.
It is recommended that SVG files have the extension
".svg"
(all lowercase) on all platforms. It is
recommended that gzip-compressed
[RFC1952]
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 1.1 namespace, public identifier
and system identifier:
- SVG Namespace:
- http://www.w3.org/2000/svg
- Public Identifier for SVG 1.1:
- PUBLIC "-//W3C//DTD SVG 1.1//EN"
- System Identifier for the SVG 1.1 Recommendation:
- http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd
The following is an example document
type declaration for an SVG document:
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
Note that DTD listed in the System Identifier is a
modularized DTD (i.e. its contents are spread over multiple
files), which means that a validator may have to fetch the
multiple modules in order to validate. For that reason,
there is a single flattened DTD available that corresponds
to the SVG 1.1 modularized DTD. It can be found at
http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-flat.dtd.
While a DTD is provided in this specification, the use of DTDs for
validating XML documents is known to be problematic. In particular, DTDs
do not handle namespaces gracefully. It is not recommended that
a DOCTYPE declaration be included in SVG documents.
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 IRI
referencing and requires support for base IRI specifications
defined in XML Base
[XML-BASE].
- SVG content can be styled by either CSS (see
Cascading Style Sheets (CSS) level 2
[CSS2]) or XSLT
(see XSL Transformations (XSLT) Version 1.0
[XSLT] and
XSL Transformations (XSLT) Version 2.0
[XSLT2]).
See Styling with CSS and
Styling with XSL for details.
- 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
DOM Level 2, including the CSS object model and event
handling
[DOM2]
[DOM2STYLE]
[DOM2EVENTS].
- 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™ 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.
Also, see Accessibility Support.
In environments which support
DOM 2 Core
[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 Key words for use in RFCs to Indicate Requirement Levels
[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
- animation element
- An animation element is an element that can be used to animate
the attribute or property value of another element. The following elements
are animation elements: ‘animateColor’, ‘animateMotion’, ‘animateTransform’, ‘animate’ and ‘set’.
- animation event attribute
- An animation event attribute is an event attribute that specifies
script to run for a particular animation-related event. See
Animation event attributes.
The animation event attributes are ‘onbegin’, ‘onend’, ‘onload’ and ‘onrepeat’.
- basic shape
- Standard shapes which are predefined in SVG as a
convenience for common graphical operations. Specifically:
‘circle’, ‘ellipse’, ‘line’, ‘polygon’, ‘polyline’ and ‘rect’.
- 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:
‘a’, ‘defs’, ‘glyph’, ‘g’, ‘marker’, ‘mask’, ‘missing-glyph’, ‘pattern’, ‘svg’, ‘switch’ and ‘symbol’.
- conditional processing attribute
- A conditional processing attribute is one that controls whether
or not the element on which it appears is processed. Most elements,
but not all, may have conditional processing attributes specified
on them. See Conditional processing
for details. The conditional processing attributes defined in
SVG 1.1 are ‘requiredExtensions’, ‘requiredFeatures’ and ‘systemLanguage’.
- core attributes
- The core attributes are those attributes that can be specified
on any SVG element. See Common attributes.
The core attributes are ‘id’, ‘xml:base’, ‘xml:lang’ and ‘xml:space’.
-
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.
- descriptive element
- An element which provides supplementary descriptive information about
its parent. Specifically, the following elements are descriptive elements:
‘desc’, ‘metadata’ and ‘title’.
- document event attribute
- A document event attribute is an event attribute that specifies
script to run for a particular document-wide event. See
Document-level event attributes.
The document event attributes are ‘onabort’, ‘onerror’, ‘onresize’, ‘onscroll’, ‘onunload’ and ‘onzoom’.
- event attribute
- An event attribute is one that specifies some script to run when
an event of a certain type is dispatched to the element on which the attribute
is specified. See Event attributes.
- fill
- The operation of painting the interior of a shape or the interior of the
character glyphs in a text string.
- filter primitive attributes
- The filter primitive attributes is the set of attributes that are common
to all filter primitive elements. They are
‘height’, ‘result’, ‘width’, ‘x’ and ‘y’.
- filter primitive element
- A filter primitive element is one that can be used as a child of a
‘filter’ element to specify a node in the filter graph.
The following elements are the filter primitive elements defined
in SVG 1.1:
‘feBlend’, ‘feColorMatrix’, ‘feComponentTransfer’, ‘feComposite’, ‘feConvolveMatrix’, ‘feDiffuseLighting’, ‘feDisplacementMap’, ‘feFlood’, ‘feGaussianBlur’, ‘feImage’, ‘feMerge’, ‘feMorphology’, ‘feOffset’, ‘feSpecularLighting’, ‘feTile’ and ‘feTurbulence’.
- 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.
- gradient element
- A gradient element is one that defines a gradient paint server.
SVG 1.1 defines the following gradient elements: ‘linearGradient’ and ‘radialGradient’.
- graphical event attribute
- A graphical event attribute is an event attribute that specifies
script to run for a particular user interaction event. See
Event attributes on graphics and container elements.
The graphical event attributes are ‘onactivate’, ‘onclick’, ‘onfocusin’, ‘onfocusout’, ‘onload’, ‘onmousedown’, ‘onmousemove’, ‘onmouseout’, ‘onmouseover’ and ‘onmouseup’.
- graphics element
- One of the element types that can cause graphics to be
drawn onto the target canvas. Specifically:
‘circle’, ‘ellipse’, ‘image’, ‘line’, ‘path’, ‘polygon’, ‘polyline’, ‘rect’, ‘text’ 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: ‘image’ and ‘use’.
- IRI reference
-
An IRI reference is an Internationalized Resource Identifier
with an optional fragment identifier, as defined in
Internationalized
Resource Identifiers
[RFC3987].
An IRI reference serves as a reference to a resource or (with a
fragment identifier) to a secondary resource. See
References and the ‘defs’ element..
- lacuna value
A lacuna value is a defined behavior used when an attribute or
property is not specified, or when an attribute or property has an unsupported value.
The lacuna value is to be used for the purposes of rendering and calculating
animation values.
For lacunae which are properties, if the property is inherited and
there is no inherited value (for example, on the root element), the
lacuna value is the
initial value
as specified in the definition of that property
([CSS2], section 6.1.1).
For non-inherited properties, the lacuna value is always the initial value.
Note that a lacuna value is distinct from the XML term
default value,
which uses DTD lookup to determine whether an attribute is required
and what its value is, and inserts required attributes and their
values into the DOM
([XML10], section 3.3.2).
Lacuna values are not visible in the DOM, and cannot be
accessed with DOM methods such as getAttribute.
At the XML parser level, SVG does not have default values;
lacunae are part of the SVG application layer, and their values are
derived from the UA.
- light source element
- A light source element is one that can specify light source
information for an ‘feDiffuseLighting’ or ‘feSpecularLighting’
element. The following light source elements are defined in SVG 1.1:
‘feDistantLight’, ‘fePointLight’ and ‘feSpotLight’.
- local IRI reference
- An Internationalized Resource Identifier [RFC3987] that does
not include an <absoluteIRI> or <relativeIRI> 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 IRI reference
- An Internationalized Resource Identifier [RFC3987] that
includes an <absoluteIRI> or <relativeIRI> and thus
(usually) represents a reference to a different document or
an element within a different document. See References and the ‘defs’ element.
-
outermost svg element
-
The furthest ‘svg’ ancestor element that remains in the current
SVG document fragment.
- 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’ and
‘polygon’.
- stroke
- The operation of painting the outline of a shape or the outline of
character glyphs in a text string.
- structural element
- The structural elements are those which define the primary
structure of an SVG document. Specifically, the following
elements are structural elements:
‘defs’, ‘g’, ‘svg’, ‘symbol’ and ‘use’.
- 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
- A text content element is an SVG element that causes a text string
to be rendered onto the canvas. The SVG 1.1 text content elements are the
following: ‘altGlyph’, ‘textPath’, ‘text’, ‘tref’ and ‘tspan’
- text content child element
- A text content child element is a text content element that is allowed
as a descendant of another text content element. In SVG 1.1,
the text content child elements are the following:
‘altGlyph’, ‘textPath’, ‘tref’ and ‘tspan’
- 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.
- 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.
- XLink attributes
- The XLink attributes are the seven attributes defined in
the XML Linking Language
specification [XLINK], which are used
on various SVG elements that can reference resources. The most
import XLink attribute is ‘xlink:href’,
whose definition can be found on each element that allows it.
The remaining XLink attributes are ‘xlink:type’, ‘xlink:role’,
‘xlink:arcrole’, ‘xlink:title’, ‘xlink:show’ and
‘xlink:actuate’.