Re: Action-1634: the switch element and <title> and <desc>

Second thoughts on title and desc:

In HTML, the title attribute can be used to create the accessible
description if it is not used as the accessible name.  We should explicitly
define the same behavior for SVG.

In other words, if the author specifies aria-label or aria-labelledby, use
that for the name, but if they also include a <title> element (as a tooltip
for visual users), that should be used as the description if no other
description is provided.  This would support the common practice in data
visualizations of using title tooltips to provide additional information,
such as the numerical data.

For example, in a bar chart, the bars should have aria-labelledby pointing
to the visible axis labels.  However, they could also have a title tooltip
giving the exact numerical value represented by the height of the bars.
That should be used for the accessible description.

The revised text would be as follows:

Otherwise, unless the element is marked as presentational
(role="presentation" or role="none"):


   - If performing a text alternative computation for an accessible name
   and the current node provides a descendant <title> element chosen based on
   the language rules for the SVG specification, return the <title>
   element's text content as a flat string.
   - If performing a text alternative computation for an accessible
   description, and the current node provides a descendant <desc> chosen based
   on the language rules for the SVG specification, return the concatenated
   text and child content of that <desc> element.  If there is no <desc>
   element, but the node provides a descendant <title> element (chosen
   based on the language rules for the SVG specification) that was not used
   as the accessible name, return the <title> element's text content.