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Re: Ambiguities in fill:url() / stroke:url() syntax

From: Robert O'Callahan <robert@ocallahan.org>
Date: Mon, 29 Oct 2012 00:08:59 +1300
Message-ID: <CAOp6jLbpj3Mgu=+J1qty72bXiTWp=qCoUAWzRL9GsEndVh4EcA@mail.gmail.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: Dirk Schulze <dschulze@adobe.com>, www-svg <www-svg@w3.org>, www-style <www-style@w3.org>
On Sun, Oct 28, 2012 at 11:33 PM, Tab Atkins Jr. <jackalmage@gmail.com>wrote:

> On Sun, Oct 28, 2012 at 11:20 AM, Robert O'Callahan
> <robert@ocallahan.org> wrote:
> > On Sun, Oct 28, 2012 at 11:04 PM, Tab Atkins Jr. <jackalmage@gmail.com>
> > wrote:
> >> I don't have any better ideas besides "just do everything right".
> >
> > What does that mean?
>
> It means ::handwave:: and just magically work correctly depending on
> whether you're linking to a paint source or not.
>

Still not a very satisfying answer. :-)

The issue is especially complicated because I think the way you load the
document --- whether as an external resource document, or as an image ---
could affect whether you're linking to a paint server or not; if not now,
then in the future as Web standards evolve. For example, we currently
restrict subresource URIs in SVG documents to URIs that don't load other
resources --- i.e., data: and blob: (for security reasons). But we don't
restrict subresource URIs in external resource documents that way. So if
there was ever a situation where the success or failure of a subresource
load in foo.svg could affect the type of element referenced by foo.svg#abc,
you could construct a document foo.svg where what foo.svg#abc refers to
depends on whether you loaded it as an external resource document or an
image. Now I can't actually think of a way this could happen today, but I
can think of lots of "near misses" --- for example, if we allowed scripting
in either external resource documents or SVG images, or if we allowed Web
Components in either, or if we had a transclusion feature that let you load
content directly into a document, or if we allowed dynamic loading of DTDs.

Additional complications arise if what is referenced by foo.svg#abc can
change over time, e.g. while foo.svg loads, or if <meta refresh> is allowed
in SVG images or external resource documents, or if the "id" attribute can
be animated in any way, or you're able to dynamically modify the DOM of an
external resource document or an SVG image document in any way. Then we
could get into situations where UA is "linking to a paint source" so
treating the URI as an external resource reference, then suddenly it isn't.
Or vice versa. We have to reload the document in a different way? Or
something.

By the way, if someone created an document foo.svg with a paint server
element whose ID is "xywh=0,0,10,10", how would your magical approach treat
url(foo.svg#xywh=0,0,10,10)? :-)

Rob
-- 
“You have heard that it was said, ‘Love your neighbor and hate your enemy.’
But I tell you, love your enemies and pray for those who persecute you,
that you may be children of your Father in heaven. ... If you love those
who love you, what reward will you get? Are not even the tax collectors
doing that? And if you greet only your own people, what are you doing more
than others?" [Matthew 5:43-47]
Received on Sunday, 28 October 2012 11:09:27 GMT

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