Re: minutes, SVG WG London F2F 2014 minutes, day 3

On Tue, Aug 26, 2014 at 4:39 AM, Cameron McCormack <cam@mcc.id.au> wrote:

>
>
   krit: external resources are not supported for the most part in
>    Blink/WebKit
>
>    Rossen_: IE will implement them
>    ... animations not running would be much simpler
>    ... can we make the case for not running them?
>

We've had extensive discussions about how external resources should work,
on #whatwg and across various mailing lists. The consensus (between me,
Tab, Anne, krit and everyone else I've managed to drag in) is that external
resource document loads should be exactly the same as SVG image loads. I
apologize for not ensuring this is written down in a spec.

The main reason is to solve the ambiguity problem where CSS rules like
"mask:url(foo.svg#bar)" could be either an external resource reference to
the paint-server #bar in foo.svg, or an SVG image foo.svg with #bar as the
active element (see SVG image stacks). If the load step behaves differently
in these two cases, then the ambiguity is very difficult to resolve
satisfactorily. If the load step is the same for both cases, then it's
easy: we can check whether the #bar element is a paint server (<pattern>
etc); if it is --- and the resource is same-origin --- we treat the url()
as an external resource reference, otherwise we treat it as an SVG image.

Implications:
-- External resource documents must be stand-alone resources, obeying the
same restrictions as SVG images. In particular an external resource
document can only reference another external resource document through a
data: or blob: URI. It is not possible to create cyclic references between
external resource documents, but it is possible for multiple external
resource documents to reference a common external resource document via a
blob: URI.
-- External resource documents should run animations, since SVG images do.
-- The animation timeline rules for external resource documents should be
the same as SVG images.

Really, the goal is for "external resource documents" as a concept to go
away and we'll just have SVG image documents which can also be the target
of external resource references.

This is a change in Gecko behavior, but we'll fix Gecko. It should not
create any Web compatibility issues since Webkit/Blink don't implement
external resources yet. It simplifies things from the spec point of view;
external resource references have never been properly specced anyway. Most
use cases for external resource references will continue to work.

Rob
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