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Re: UA: indicate missing content

From: Helder Magalhães <helder.magalhaes@gmail.com>
Date: Sat, 26 Jul 2008 11:43:44 +0100
Message-ID: <2a1ddf8a0807260343w11b0a913h361a5a3f971d9779@mail.gmail.com>
To: "Jonathan Chetwynd" <j.chetwynd@btinternet.com>
Cc: www-svg <www-svg@w3.org>

> current UA do not indicate missing content either with graphic or text.
> iirc batik wont display at all, others ignore.
> Is there a recommendation on this issue?
[...]
> html UA generally provide an empty box with a cross or similar and alt
> content

The external resources property [1] seems to imply a recommendation on
this: error processing notes [2] states that:
«A highly perceivable indication of error shall occur. For visual
rendering situations, an example of an indication of error would be to
render a translucent colored pattern such as a checkerboard on top of
the area where the SVG content is rendered.»

I'd interpret the whole as: if a document portion is marked with
"externalResourcesRequired" set to "true" and the external resource(s)
is(are) not available, then mark that portion with a checkerboard (or
similar). Please correct me if this sounds naive!

So, if your findings are correct (didn't check implementations
myself), user agents seem to be the ones which need to catch up. ;-)

As an implementation suggestion, one might use conditional processing
[3] to achieve a desired fall back. Using a "switch" containing
external resources required feature string [4] for UA which support
external resource loading (with proper error processing) and
alternative content for cases (where the UA doesn't contain the
feature string) might do the trick! :-)



> I recognise the SVGWG may not be chartered to consider UA issues, however
> and there does not seem to be another suitable public space to raise this.

I believe the SVGWG is the proper place for discussing user agent
matter (which relates to SVG, of course). For instance, there are
guidelines for user agent behavior spread over the specification (for
example, in implementation notes section [5]).



Hope this helps,

 Helder Magalhães

[1] http://www.w3.org/TR/SVG/struct.html#ExternalResourcesRequired
[2] http://www.w3.org/TR/SVG/implnote.html#ErrorProcessing
[3] http://www.w3.org/TR/SVG/struct.html#ConditionalProcessing
[4] http://www.w3.org/TR/SVG/feature.html#ExternalResourcesRequired
[5] http://www.w3.org/TR/SVG/implnote.html
Received on Saturday, 26 July 2008 10:44:19 GMT

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