Appendix B. SVG Glossary

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The purpose of this glossary is twofold. First, it helps you understand terms used in this book. Second, as you move beyond the scope of this book, this glossary provides a foundation to aid you in understanding other documents describing technical issues relating to SVG.

Words appearing in italics within the definitions indicate that those words are defined elsewhere in this glossary.

Animation Target

The attribute that is the target of an SVG animation. The animation target is designated by assigning an appropriate value to the attributeName attribute.

Attribute

A way of describing a characteristic of an SVG element. Attributes must conform to XML syntax requirements, with the form attribute="value" or attribute='value'. You have a choice whether to use double or single quotes, but you must use only one of these on any individual attribute. If you fail to use quotes, the SVG document is not well formed.

Basic Shapes

Predefined common graphical shapes that include the <rect>, <circle>, <ellipse>, <line>, <polyline>, and <polygon> elements.

Canvas

The space (potentially infinite) where an SVG image can be rendered. In practice, the rendering of SVG occurs in a finite rectangular area of the canvas the viewport.

CDATA Section

An XML section designed to contain character data, not intended to be parsed as XML. One use in SVG is within a <style> element to contain an internal style sheet.

Container Element

An element that can have graphics elements and other container elements as child elements. The SVG container elements are <svg>, <g>, <defs>, <symbol>, <clipPath>, <mask>, <pattern>, <marker>, <a>, and <switch>.

Document

A well-formed XML document that describes an SVG image. The document may contain or link to other images, in either SVG or other formats.

Document fragment

In SVG, consists of any number of SVG elements contained within an <svg> element.

Document Object Model

A representation of the structure of an SVG image that provides an application programming interface (API) accessible by scripting languages, such as JavaScript.

Element

A basic unit of the structure of an XML and SVG documents that can possess attributes. An element has start and end tags, in pairs, or can be expressed as an empty element tag.

Fill

An attribute of many SVG elements that defines how an SVG shape other than the stroke will be painted inside the path defining the shape.

Filter

In SVG, a series of graphical operations that produce a new visual appearance built up by applying to graphics elements a range of mathe-matically based filter primitives within an SVG <filter> element. Examples of SVG filter effects are drop shadow and bevel.

Filter Primitive

A graphical operation that forms part of an SVG filter, represented as an SVG element, such as <feGaussianBlur> or <feMerge>. Filter primitives can be combined in a variety of ways to produce sophisticated filter effects.

Global Attributes

A series of XLink attributes available for use on any SVG element. The attributes are xlink:type, xlink:href, xlink:actuate, xlink:show, xlink:role, xlink:title, and xlink:arcrole.

Graphics Element

One of the element types that can cause graphics to be drawn on the target SVG canvas. They include but are not confined to SVG shapes. Available graphics elements are <circle>, <ellipse>, <image>, <line>, <path>, <polygon>, <polyline>, <rect>, <text>, and <use>.

Graphics Referencing Element

A graphics element that uses a reference to a different document or file (SVG or other format) or to an SVG element as the source of its graphical content. SVG 1.0 provides two graph-ics-referencing elements: <image> and <use>.

Original Value

The value maintained in the Document Object Model, or DOM, during an SVG animation. A separate presentation value is used to produce the changing visual appearance onscreen.

Paint

Paint represents how color is presented on the SVG canvas. SVG supports three types of paint: color, gradients, and patterns. Paint includes both color and alpha values.

Painter's Model

A conceptual picture of the way in which an SVG rendering engine (viewer) "paints" or re-creates an SVG image. It has some similarities to the effect of applying oil paint on a canvas.

Path

A mathematical description of the outline of an SVG shape. In addition to the predefined basic shapes, it can be represented by the <path> element (see Chapter 3).

Presentation Attributes

Styling in SVG can be added inline using the style attribute or individual presentation attributes, such as fill and font-family.

Presentation Value

The value of an attribute that is used to define the visual appearance at any moment during an SVG animation. The presentation value that changes as a function of time. A separate original value of the attribute is maintained in the Document Object Model.

Shape

A graphics element that is defined by some combination of straight lines and curves. In SVG, the shapes provided are <circle>, <ellipse>, <line>, <path>, <polygon>, <polyline>, and <rect>.

String

A sequence of characters that may be rendered within an SVG <text> element.

Stroke

The paint applied to the outline of an SVG shape or characters in a text string. The stroke attribute can specify paint type, width, opacity, and other characteristics that affect the appearance of an object.

SVG

Scalable Vector Graphics.

Viewport

The rectangular area where SVG is rendered; part of the potentially infinite SVG canvas.

Viewport Coordinate System

The coordinate system within the current viewport.

Viewport Space

A synonym for viewport coordinate system.

W3C

World Wide Web Consortium, an international cross-industry organization that helps develop and promote vendor-neutral technology standards for the Web.

Well-formed

A term to describe an SVG (or other XML) document that complies with the syntax required by the XML 1.0 Recommendation. For example, elements must be properly nested within each other, and attribute values must be enclosed in quotes.

XML

Extensible Markup Language. SVG is an application of XML and therefore uses the syntax required by the XML 1.0 Recommendation.

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