ARIA spec: State change notification query

Could somebody please clarify the following statement made at the end of
section 6.5.1 relating to user agent notification of state changes found at:

http://www.w3.org/TR/wai-aria/states_and_properties#aria-controls 

The statement says:

Widget attributes might be mapped by a user agent to platform accessibility
API states, for access by assistive technologies, or they might be accessed
directly from the DOM. User agents MUST provide a way for assistive
technologies to be notified when states change, either through DOM attribute
change events or platform accessibility API events.

I'm curious to know how screen reader developers for example are supposed to
interpret this statement as it seems a little vague to me. I.e. How do the
screen reader developers know whether to leverage the accessibility API or
ignore the accessibility API and use DOM events to communicate any changes
to the user?

If I were using this information to implement a screen reader then the only
way I can see that this could be sensibly implemented would be to use both
approaches on the assumption that the UA will support one of them. The
statement does say that the UA should either support notifications through
accessibility API or DOM events which would seem to be clear enough but if
UA developers were to provide both mechanisms, AT would provide the same
information twice.

Is this a potential problem and should the statement be qualified by saying
that UA should support notifications via the accessibility API or DOM
events, but not both?

Thoughts appreciated.

Cheers
Ian

Received on Wednesday, 20 March 2013 14:08:25 UTC