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Missing src on img/audio/video and fallback content

From: Philip Jägenstedt <philipj@opera.com>
Date: Fri, 20 Jun 2008 19:58:15 +0700
To: HTML WG <public-html@w3.org>
Message-Id: <1213966695.12390.23.camel@localhost>

Hi!

A missing src attribute on img is defined by
http://www.w3.org/html/wg/html5/#the-img

"If the src attribute is omitted, the image represents whatever string
is given by the element's alt attribute, if any, or nothing, if that
attribute is empty or absent."

However, it's less clear to me what should happen for audio/video
elements.

http://www.w3.org/html/wg/html5/#video

"If the element has a src attribute: transparent.
If the element does not have a src attribute: one or more source
elements, then, transparent."

In other words, undefined when neither (valid) src attribute or source
element is given? This is said about content in video/audio element:

"Note: In particular, this content is not fallback content intended to
address accessibility concerns. To make video content accessible to the
blind, deaf, and those with other physical or cognitive disabilities,
authors are expected to provide alternative media streams and/or to
embed accessibility aids (such as caption or subtitle tracks) into their
media streams."

That's fine, but what is the fallback when there is no src/source. There
are several options, and I'm not sure how others are implementing.

1. display nothing (equivialent to css display:none)
2. display a 300x150 px transparent box
3. display a small icon, red X or similar

Is this the kind of thing that should be specified in error handling in
HTML 5, or is it completely up to the user agent?

-- 
Philip Jägenstedt
Opera Software
Received on Friday, 20 June 2008 15:27:06 GMT

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