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.