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Re: 15.1.2 Navigation

From: Jean-Claude Dufourd <jean-claude.dufourd@streamezzo.com>
Date: Thu, 11 Nov 2004 12:16:01 +0100
Message-ID: <419349F1.7000008@streamezzo.com>
To: Doug Schepers <doug@schepers.cc>
Cc: www-svg@w3.org

Hi Doug

Doug Schepers wrote:

>Directional navigation seems a little confusing. Am I understanding it
>correctly to say that nav-up, nav-down, nav-left, and nav-right depend on
>the document order?
>
No, it does not.
When *nav-index* is not specified, "TAB"-like navigation among focusable 
elements is in document order, but that is it for document order.

>I appreciate that this is a property inherited from CSS, but CSS had HTML as
>its use case, which is a document format in which elements and text defined
>at the beginning of the document most typically will be visually depicted at
>the top of the page, and in which the document and location order of those
>elements rarely changes. This is far from the case with SVG.
>
>Consider:
><svg>
>  <circle id="c1" focusable="true" cx="300" cy="500" ... />
>  <rect id="r1" focusable="true" x="100" y="100" ... />
>  <circle id="c2" focusable="true" cx="50" cy="50" ... />
></svg>
>
>If the current focus were on Rectangle 'r1', and the user pressed the up
>arrow key, triggering a nav-up event, the focus would shift to Circle 'c1',
>which is earlier in the document order but "down" in the visual field. This
>is compounded by the fact that often elements are repositioned dynamically,
>making the authoring of a document that has consistent behavior regards
>directional navigation via document order vs. visual location impossible.
>  
>
Directional navigation by visual location only was considered and 
rejected, because you never know what to do in the case of e.g. tables 
with some merged cells, or some large object above two small ones (where 
would 'down' leave you then ?)

nav-up/down/left/right is not directional navigation, per se.
It just allows the author to define which other object should be 
focussed after the current one, should the virtual UP key be pressed (I 
say virtual, because it can be mapped to cursor key, or joystick or 
something else)
If indeed the objects are repositionned dynamically, then the author 
should not use nav-* (or update the values together with the positionning)
Best regards
JC

--
*Jean-Claude Dufourd*
Chief Scientist, *Streamezzo*
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Received on Thursday, 11 November 2004 11:17:30 UTC

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