Modification to the role attribute definition

I modified the definition of the role attribute to not be limited to
rendered elements. We should not limit these to rendered elements.

Unlike HTML, virtually all of SVG does not have strong native host language
semantics where we would need to restrict the use of role value.
Consequently, there is not a lot of value creating a strong native host
language mapping table like we did in HTML. In HTML we chose to produce an
entire table that state what roles could be applied to what elements and
what would not. However, like HTML there are some SVG elements where we
would have not intention of mapping them to a specific role on a platform
accessibility API. HTML5 calls these elements has having "no role". In this
case ARIA considers these as having role of "presentation" and would not be
mapped to platform accessibility API. Examples of this in HTML5 would be
<title> and <script>. Examples of these in SVG would be <title> and <desc>
which would be used in the computation of the name and description of an
element which would have a role value. So, rather than having a mapping
table I chose to limit the SVG elements which support the role attribute.

Please review the new definition:
https://svgwg.org/svg2-draft/struct.html#roleattribute

The SVG elements for which we allow the role attribute are currently
defined in the SVG attribute index
https://svgwg.org/svg2-draft/attindex.html
Also each element that specifies aria attributes has the role attribute
included in the list.

I need to look at issues 39 and 40. Note: we could refer to the Role
attribute module: http://www.w3.org/TR/role-attribute/

Related to this discussion, we agreed to produce and SVG 2.0 User Agent
Implementation Guide along with a Core (Mostly the ARIA User Agent
Implementation Guide today) and an HTML 5.1 User Agent Implementagion
Guide. These guides provide normative mappings to platform accessibility
API services. We have to determine who will work on these.

Rich


Rich Schwerdtfeger