Draft Revisions to Canvas 2D Context API

Sorry it took so long for me  to get this draft out. Too much traveling
going on. Please take a look and provide feedback.

The edits reflect:

- Separate caret/selection from drawFocusRing
http://lists.w3.org/Archives/Public/public-html/2010Mar/0502.html. The Mac
does not support caret tracking during selection so this needed to be
allotted for.
- Expose the caret blink rate via 2D canvas API. Frank indicated Windows
has a 500 millisecond defult blink rate a. Carl Carlson (Apple) indicated a
default blink rate of 560 milliseconds. I provided information for authors
regarding average default blink rates should the value returned be negative
1.
- Change the name of canDrawCustom and clean up its definiton which
according to Maciej is "want to draw custom unless Special Focus Ring
Setting is in Effect"
http://lists.w3.org/Archives/Public/public-html/2010Mar/0363.html


David Bolter: From the Firefox perspective we still need to see that the
caret/selection location can be properly mapped to the accessibility API as
is. Currently, the caret position is a logical one in IA2 and I believe the
caret pixel position is calculated from the character font offset and the
bounding rectangle of the text. We may need to move the system caret. I am
trying to find the old Windows API for that.

Frank: Please see if we can map the pixel position accurately, when
provided, from the accessibility API. Windows used to have an MSAA
notification for driving a  magnifier based on screen position. I don't
know if this is still used when using UIA Express.

Maciej or James: Same question for Mac regarding the caret/selection
position.

(See attached file: 2dcontext10-Apr-11.html)

Rich Schwerdtfeger
CTO Accessibility Software Group