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Re: Fw: Web site accessibility-layers

From: David Woolley <david@djwhome.demon.co.uk>
Date: Wed, 16 Apr 2003 22:31:09 +0100 (BST)
Message-Id: <200304162131.h3GLV9T08470@djwhome.demon.co.uk>
To: w3c-wai-ig@w3.org

> 
> >"Layers" is a feature of HTML and CSS that allows content that is

Layers is a dead end technology in Netscape 4.x, mainly used for
animation with scripting.

The nearest W3C technology is absolute positioning in CSS.

> >arranged logically in a document to be displayed visually in another
> >layout.  There are layer codes (z-index) that determine which layer is
> >on top, and which is under.  By setting the z-index, presentation order
> >can be changed.

z-index is not relevant to presentation order.  It's main use is for
animations, popup menus and tabbed dialogue type display - all, of
necessity, involving client side scripting.  The last two are basically
about selecting what is presented, not about changing its order.  The only
non-scripting use would be rather artistic layouts, where non-background
items are deliberately overlapped.

> >In the background, layers are created using the <div></div E markup,
> >which will be ignored by many types of assistive technologies.  This is
> >what allows accessible pages to be created with layers - they can be
> >invisible to those who need access.

CSS positioning is not restricted to DIV elements, although NS4 layers
have a special element and CSS positioning on NS4 is likely only to
work on DIVs, where it can be internally converted to LAYER (it doesn't
work well even then).

More importantly, this paragraph reflect what is probably the dominant
design approach (design the layout then force the HTML and CSS to
produce it), but the right way of thinking about it is that you construct
the document in a logical reading order, then position parts of it 
to get a particular presentation.

> >makes sense.  This is where many designers can mess things up.  The
> >page should be designed first so that the content is in logical order,

OK. That point was already made.

> >then the layers used to provide the desired visual presentation, with
> >the awareness that not everyone will see the "visual" order.
Received on Thursday, 17 April 2003 01:48:39 GMT

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