2 Introduction to SVG

This section will provide an introduction to the various concepts, approaches and features that make up SVG. It will probably be quite lengthy. So far, only the following introductory sections have been written:

• 2.1 SVG MIME Type
• 2.2 Compatibility with Other Standards Efforts
• 2.3 Two Indended Uses: Documents and Fragments
• 2.4 Accessibility Features
• 2.5 Fonts

2.1 SVG MIME Type

The MIME type for SVG will be "image/svg". The W3C will register this MIME type around the time which SVG is approved as a W3C Recommendation.

2.2 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.

Here are some of the ways which SVG fits in and conforms to other standards:

• SVG is an application of the XML 1.0 Recommendation
• SVG conforms to the XML Namespace Recommendation
• SVG is tracking and will conform with XLink and XPointer (once these specifications become Recommendations)
• SVG conforms to the Cascading Style Sheets (CSS) level 2 Recommendation
• SVG conforms to the Document Object Model (DOM) level 1 Recommendation and is tracking the DOM level 2
• SVG utilises the switch and test concepts from the SMIL 1.0 Recommendation.
• SVG attempts to fit in with the HTML version 4 Recommendation, and is meant to work as a component grammar with future versions of HTML which are expressed in XML as a set of component XML grammars

Because SVG conforms to DOM, it will be scriptable just like HTML version 4 (sometimes called DHTML). This will allow a single scripting approach to be used simultaneously for both XML documents and SVG graphics. Thus, interactive and dynamic effects will be possible on multiple XML namespaces using the same set of scripts.

2.3 Two Indended Uses: Documents and Fragments

SVG supports two intended uses:

• Stand-alone SVG files which represent complete drawings. These stand-alone SVG files might have been created by a graphics authoring program. If destined to be part of a Web page, these files might be included/referenced using XPointer by a parent document such as an XML Web page.
• SVG "fragments" which represent snippets of graphics which are interspersed (often inline) among the content of a parent document such as an XML Web page.

The following shows a trivial stand-alone SVG file with no content:

<?xml version="1.0" standalone="yes"?>
<svg width="4in" height="3in"
 xmlns = 'http://www.w3.org/Graphics/SVG/svg-19990412.dtd'>
 <!-- Insert drawing elements here -->
</svg>

Download this example

The simplest drawings can be described by a sequence of drawing elements. The following example draws a rectangle:

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG April 1999//EN" 
  "http://www.w3.org/Graphics/SVG/svg-19990412.dtd">
<svg width="4in" height="3in">
  <desc>This is a rectangle
  </desc>
  <g>
    <rect x="20" y="30" width="100" height="80"/>
  </g>
</svg>

Download this example

The following shows how a fragment from the SVG namespace could be interspersed into a parent XML grammar:

<?xml version="1.0"?>
<ABC xmlns="http://parent.name.space"
     xmlns:svg="http://www.w3.org/Graphics/SVG/1.0">
  <!-- document in the parent namespace -->
  <svg:svg width="40%" height="40%">
     <svg:rectangle width="43.6" height="31.5"/>
     <!-- svg graphic continues -->
   </svg:svg>
   <!-- document in parent namespace continues -->
</ABC>

Download this example

2.4 Accessibility Features

Drawings done in SVG will be much more accessible that drawings done as image formats for the following reasons:

• Text strings in SVG are represented as regular XML character data rather than bits in an image. (See Text.)
• At any place in the SVG hierarchy, a drawing can include a long set of descriptive text and/or a short description in the form of a title. Both of these features can be used to help the visually impaired interpret both the intent and specific content of a drawing. The drawing can be architected such that there is a single description for the drawing as a whole or there are multiple descriptions which are distributed within the drawing and describe each separate component within the drawing.
• Because of SVG's support of Cascading Style Sheets Level 2 (??? need to add link), there will be the ability to set up personal style sheets to adjust the color contrast of graphic elements.
• Because SVG documents are scalable, people with partial visual impairment will be able to zoom in on graphics for easier viewing.

2.5 Fonts

Reliable delivery of fonts is considered a critical requirement for SVG. Designers should be able to create SVG graphics with whatever fonts they care to use and then the same fonts should appear in the end user's browser when viewing an SVG drawing, even if the given end user hasn't purchased the fonts in question. This parallels the print world, where the designer uses a given font when authoring a drawing for print, but when the end user views the same drawing within a magazine the text appears with the correct font.

The current plan for SVG is to rely on CSS2's WebFont facility for delivery of font data to end users.

A companion approach would be add a simple font facility directly into SVG so that SVG drawings could carry around their own font data. Currently, this simple font facility is not part of SVG.

The SVG working group is particularly interested in public feedback on SVG's approach to fonts.