Draft Alert Dialog or Message Dialog design pattern

[ZoeBijl]

A dialog with the primary purpose of communicating a message and acquiring a user response to that message.

Alert Dialog or Message Dialog in the APG

[mcking65]

Remove the role="document" requirement from the message. It is unnecessary.

Note: this was also noted by feedback provided in issue #48.

[mcking65]

Proposed text for resolving this issue can be seen in the editors draft at:
http://w3c.github.io/aria-practices/#alertdialog

[jasonjgw]

The implication is that a typical alert dialog with a "close" button will have focus initially set to the button, but aria-describedby will encourage AT to read the alert message. I think this will be clearer to developers when the example is in place.

[mcking65]

@jasonjgw, that is correct.

[mcking65]

Closing issue based on review in September 12, 2016 APG meeting.