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Added introduction to Graphics AAM #384

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<section id="sotd"> </section>
<section id="intro" class="informative">
<h2>Introduction</h2>
<p>
In traditional Graphical User Interface (GUI) applications,
components of the User Interface (UI) are
displayed when needed and hidden when not needed
based on user interactions.
<a class="termref" data-lt="Accessibility API">Accessibility API</a>s are used to communicate
<a class="termref" data-lt="Semantics">semantics</a>
about the user interface to
<a class="termref" data-lt="Assistive Technologies">assistive technologies</a>
used by people with disabilities.
These <abbr title="application programming interfaces">APIs</abbr> constitute
a contract between applications and assistive technologies,
such as screen readers, magnifiers, alternate input devices, and speech command and control,
to enable them to access the appropriate semantics needed to produce
a usable alternative to interactive applications or complex documents.
For example, screen-reading software for blind users can determine
whether a particular <abbr title="user interface">UI</abbr> component
is a menu, button, text field, list box, etc.
It can also present the information in tables or lists
in a way that provides context for each piece of text.
</p>
<p>
For web documents and applications,
the essential semantic information is encapsulated
within the Document Object Model (<abbr title="Document Object Model">DOM</abbr>).
Assistive technologies obtain this information from the user agent,
which maps elements and attributes
to the platform Accessibility <abbr title="Application Programming Interface">API</abbr>.
</p>
<p>
In traditional <abbr title="Scalable Vector Graphics">SVG</abbr> documents,
most SVG <a class="termref" data-lt="Element">element</a>s
do not provide semantic information of value to assistive technologies.
Instead, they represent low-level vector graphics drawing directives.
That element only has meaning to assistive technologies
if the author provides alternative text, descriptions, or WAI-ARIA semantics.
</p>
<p>
To allow the author to express and dynamically update their intended semantics,
SVG 2 supports the use of
<abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> roles, states, and properties.
WAI-ARIA enables rich SVG-drawn Internet applications
to have the same accessibility features as
<abbr title="graphical user interface">GUI</abbr> applications installed on their operating system.
Authors may include
<abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> attributes in their markup
and user agents will translate it
to the platform accessibility <abbr title="application programming interfaces">APIs</abbr>.
</p>

<p>
For an introduction to <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr>,
see the <a href="http://www.w3.org/WAI/intro/aria.php"><abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> Overview</a>.
The SVG Accessibility API Mappings specification (this document)
defines how <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> features
interact with the native semantics of the SVG language.
It is part of a set of resources that define and support
the <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> specification,
including the following documents:
</p>
<ul>
<li>
<cite><a href="http://www.w3.org/TR/wai-aria-1.1/">Accessible Rich Internet Applications (WAI-ARIA) 1.1</a></cite> [[WAI-ARIA]],
a planned <abbr title="World Wide Web Consortium">W3C</abbr> recommendation
that extends the exising ARIA standard [[WAI-ARIA-10]].
It defines the core roles, states, and properties.
</li>
<li>
<cite><a href="http://www.w3.org/TR/graphics-aria-1.0/">WAI-ARIA Graphics Module</a></cite> [[GRAPHICS-ARIA]],
a planned <abbr title="World Wide Web Consortium">W3C</abbr> recommendation that defines graphics roles, states, and properties not included in <cite><a href="http://www.w3.org/TR/wai-aria-1.1/">Accessible Rich Internet Applications (WAI-ARIA) 1.1</a></cite> [[WAI-ARIA]].
</li>
<li>
<cite><a href="http://www.w3.org/TR/core-aam-1.1/">Core Accessibility API Mappings</a></cite> specification [[CORE-AAM]],
which expresses how <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr>
<a href="#dfn-role" class="termref">roles</a>, <a href="#dfn-state" class="termref">states</a>, and <a href="#dfn-property" class="termref">properties</a>
should be supported in user agents
using platform accessibility <abbr title="Application Programming Interfaces">APIs</abbr>.
</li>
<li>
<cite><a href="http://www.w3.org/TR/graphics-aam-1.0">Graphics Accessibility API Mappings</a></cite>[[GRAPHICS-AAM]], a planned <abbr title="World Wide Web Consortium">W3C</abbr> recommendation,
which expresses how <cite><a href="http://www.w3.org/TR/graphics-aria-1.0/">WAI-ARIA Graphics Module</a></cite> [[GRAPHICS-ARIA]]
<a href="#dfn-role" class="termref">roles</a>, <a href="#dfn-state" class="termref">states</a>, and <a href="#dfn-property" class="termref">properties</a>
should be supported in user agents
using platform accessibility <abbr title="Application Programming Interfaces">APIs</abbr>.
</li>

<li>
<cite><a href="http://www.w3.org/TR/accname-aam-1.1/">Accessible Name and Description: Computation and API Mappings 1.1</a></cite> [[ACCNAME-AAM]],
which outlines the specific steps user agents should follow
in order to identify accessible names (labels) and descriptions (alternative text)
for elements that are exposed to assistive technologies.
</li>
<li>
<cite><a href="http://www.w3.org/TR/wai-aria-practices/"><abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> Authoring Practices Guide</a></cite> [[ARIA-PRACTICES]],
a planned W3C Working Group Note,
which describes how web content developers can develop
accessible rich internet applications using <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr>.
It provides detailed advice and examples
directed primarily to web application developers,
yet also useful to developers of user agents and assistive technologies.
</li>
</ul>
<p>
This specification begins by providing
a general overview of accessibility <abbr title="Application Programming Interfaces">APIs</abbr>
and the hierarchy of <a class="termref" data-lt="accessible object">accessible object</a>s
known as the <a class="termref">accessibility tree</a>.
The following sections define how SVG host language elements and content &#8212;
with or without <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr>
roles, states, and properties applied &#8212;
map to accessibility <abbr title="Application Programming Interfaces">APIs</abbr>.
Other sections give guidance on calculating text alternatives,
mapping actions to <a class="termref" data-lt="role">event</a>s,
event processing, special document handling procedures, and error handling.
</p>
<p>
This guide relies heavily on the
accessibility <abbr title="Application Programming Interface">API</abbr> mappings
defined in the [[CORE-AAM]] and [[ACCNAME-AAM]] specifications
but defines changes in mappings due to features in the [[SVG]] host language.
Key areas of difference stem from the intrinsic host language semantics of SVG:
</p>
<ul>
<li>The procedure for mapping the DOM tree to the accessibility tree
is designed to simplify that tree
to only include elements with semantic importance.
</li>
<li>SVG elements are assigned default roles and properties,
which in many cases are conditional on whether they meet
the criteria for inclusion in the accessibility tree.
</li>
<li>Text computation of names and descriptions use the SVG metadata elements.
</li>
<li>Implicit ARIA states (such as whether an element is hidden) must be updated
in response to SVG animations.
</li>
</ul>

</section>
<section id="conformance" class="normative">
<p>This specification indicates whether a section is <a class="termref">normative</a> or <a class="termref">informative</a> and the classification applies to the entire section. A statement "This section is normative" or "This section is informative" applies to all sub-sections of that section.</p>
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