On 15 Feb 2007, at 02:06:11, Michael MD wrote:
Do any screen readers support some kind of metadata or semantic
markup that could be used to embed such content in the page?
No, because screen readers never actually see the markup - they're
designed to work with Windows applications that support MSAA
(Microsoft Active Accessibility), not just browsers. (After all, a
user who paid all that money for Jaws would probably be pretty
annoyed if all it could do was read web pages, but not email or Excel
spreadsheets.)
So what happens is that the application does whatever it does (e.g. a
browser parses and renders the page, Excel parses a file and builds a
visual representation of a spreadsheet) and then exposes the contents
of its display to the screen reader via the MSAA API. The screen
reader then queries the application via that API to find out what is
being displayed, and reads it out.
This is presumably why "display: none" and "visibility: hidden" don't
work, but "margin-left: -9999px" does - in the first two cases, the
element is never made a part of whatever internal representation of
the render tree IE builds for its display (this is not the same as
the DOM, by the way), whereas in the last case it _is_ included in
the internal representation, but when that representation is actually
drawn on the screen, it is in a position where Window's built-in
clipping to window boundaries means it is never seen.
So any attempt to include markup "just for screen readers" is doomed
to failure - screen readers don't use markup.
Please note that I'm not claiming to be an expert on this particular
topic, but I think this explanation covers what actually happens.
There's more info on MSAA (primarily aimed at application developers) at
<http://msdn.microsoft.com/library/default.asp?url=/library/en-us/
msaa/msaastart_9w2t.asp>
and you can get some idea of the range of applications other than web
browsers (from Access to WinZip :-) that Jaws is used with from the
dropdown list on the FAQ page:
<http://www.freedomscientific.com/fs_support/Specific_Product.cfm?
ProdID=1>
Regards,
Nick.
--
Nick Fitzsimons
http://www.nickfitz.co.uk/
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