Re: External references: how to handle 404?

Hi Boris.

Boris Zbarsky wrote:
> The real question here is this: if an SVG element references 
> http://example.com/example.svg#foo and the returned HTTP response is a 
> 404 with Content-Type image/svg+xml that contains an element with 
> id="foo", should that element be used, or should we pretend that we got 
> no document back at all?

Pretend that you got no document back at all in most cases, I think.  In
Tiny 1.2, there is this text below the reference restriction table:

  Additionally, any IRI reference which cannot be resolved is an invalid
  IRI reference. Examples of reasons for an IRI reference to be unable
  to be resolved include:
    ...
    * The IRI reference is to a resource that does not exist (for
      example, an 'image' element that references an HTTP resource that
      results in a 404 response code, even if the response body contains
      an otherwise supported raster image resource).

http://dev.w3.org/SVG/profiles/1.2T/publish/linking.html#unresolved-resources

Then, for example, the description of <use xlink:href=""> says what to
do in the case of an invalid IRI reference:

  An IRI reference to an element/fragment within an SVG document. An
  invalid IRI reference is an unsupported value. An empty attribute
  value (xlink:href="") disables rendering of the element. The lacuna
  value is the empty string.

http://dev.w3.org/SVG/profiles/1.2T/publish/struct.html#UseElementHrefAttribute

And elements with attributes that have unsupported values are processed
as if that attribute were not present.  Thus for <use xlink:href="bad"/>
you'd get no rendering.

> Robert suggests the latter, and I'm leaning that way too, but that's not 
> obvious per the spec.  For example, a local reference to #foo inside the 
> 404 document should clearly work, right?

If that 404 document is being displayed?  I suppose it should.  I don't
think 1.2T says anything about what to do when an SVG resource is
displayed (at the top level, or in an <html:object>, or whatever) when
it's the body of a 404.  The descriptions of "invalid IRI references"
are really for the case when the top level SVG document is a 2xx, and an
IRI reference within that is to a 4xx document or similar.

-- 
Cameron McCormack ≝ http://mcc.id.au/
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