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Re: ISSUE-2138 (SVG-HTML error processing): Error processing differences in SVG and HTML [Last Call: SVG 1.2 Tiny ]

From: Doug Schepers <schepers@w3.org>
Date: Thu, 16 Oct 2008 03:22:46 -0400
Message-ID: <48F6EBC6.1060800@w3.org>
To: cyril.concolato@telecom-paristech.fr
CC: SVG Working Group WG <public-svg-wg@w3.org>

Hi, Cyril-

Cyril Concolato wrote (on 10/16/08 2:56 AM):
>
>>>> * Section 5.9.1 The 'externalResourcesRequired' attribute What is the
>>>> rationale behind the sentence:
>>>> "If a node enters the error state then the document enters the error
>>>> state and progressive rendering stops." Is this behavior compatible
>>>> with traditional HTML processing? 
>>> I've identified the following error states explicitely listed in the
>>> spec:
>>> - playbackOrder='all' and use of discard
>>> - circular references
>>> - eRR true but resource not fetched
>>> - a java class listed in SVG-Handler-Class does not implement
>>> EventListenerInitializer2
>>> My problem is with the 3rd case. For example, if an image (in a group
>>> with eRR = true) is not fetched, the UA stops the rest of the rendering
>>> of the document. HTML browser don't stop rendering when an image link is
>>> broken and this is a more useful behavior. My suggestion is to say that
>>> if a node enters the error state (because of an unresolved link), then
>>> the UA should inform the user but keep rendering the rest of the
>>> document.
>>
>> I'm not sure I agree.
>>
>> The more graceful error recovery is already the behavior when
>> externalResourcesRequired="false".  externalResourcesRequired="true"
>> means exactly that: that the author considers the external resources to
>> be necessary to the proper viewing of the document.  If the author
>> wishes to allow tolerant error recovery for broken links, then they need
>> only omit the externalResourcesRequired attribute (lacuna is "false") or
>> set it explicitly to "false".  The behavior you suggest would defeat the
>> very purpose of the attribute.  externalResourcesRequired is not a
>> conditional attribute, to hide or show an element based on the
>> availability of a resource.
>>
>> If you still disagree, please let us know why you would expect the other
>> behavior, and the SVG WG will discuss it.  If this adequately explains
>> the rationale, please let us know that this is a satisfactory response.
>
> I understand your explanation, but eRR=true is actually doing 2 things:
> controlling the progressive rendering algorithm to stop the rendering
> until the resource is resolved; and controlling the resolution of the
> resources. I'm just wondering if it wouldn't be better to have 3 values:
> externalResourceRequired="none" (lacuna value, equivalent to false)
> externalResourceRequired="keep" (just pauses the rendering until the
> children are loaded but it continues rendering if a external resource
> link is broken)
> externalResourceRequired="strict" (equivalent to true in the current
> definition)
> 
> However, if you think this is too much editing or a too big change, I
> agree to leave it as is.

I do see your point, but this would be incompatible with SVG 1.1 [1],
and would indeed be too big a change to make at this point, for
relatively little gain.  We already have existing implementations, and
this would change conformance requirements.

This may be something to look at in the SVG 2.0 Core timeframe, but
since you are satisfied with the explanation as is, we will not change
it for SVG 1.2 Tiny.

[1] http://www.w3.org/TR/SVG/struct.html#ExternalResourcesRequired

Regards-
-Doug
Received on Thursday, 16 October 2008 07:22:56 GMT

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