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Re: CfC: to publish "The srcset attribute" specification as a First Public Working Draft (FPWD)

From: Edward O'Connor <eoconnor@apple.com>
Date: Tue, 05 Feb 2013 15:16:58 -0800
To: public-html-admin@w3.org
Message-id: <m2wqume4gl.fsf@eoconnor.apple.com>
Hi Fred,

You wrote:

> I object to the "The srcset attribute" specification being published
> as a FPWD on the basis that the design makes no attempt to meet many
> of use cases and requirements of the 'Use Cases and Requirements for
> Standardizing Responsive Images'

It's true that the current srcset="" specification does not currently
provide features that cover every idea contemplated in that document.

In some cases, this is because we don't have enough information. Here is
a list of all of the srcset="" bugs which have been resolved as
NEEDSINFO; if you have any information that could help us to address
these requests, please comment on the bug and reopen them!


In other cases it might simply be that we haven't finished processing
the relevant feedback. There are two open bugs on the spec:

Bug 20172 - “Art direction” use case not well supported
Bug 20176 - Syntax only supports 'mobile first'

All this is to say that this is very much a work in progress. FPWD is an
early step in the work on a specification, not the last one, and we
shouldn't expect any document to be perfect before it reaches FPWD.

I hope that you will consider retracting your objection & will work with
us post-FPWD to improve the document.

> and that the editors refuse to consider design changes that would meet
> these use cases.

I'd like to think that I'm open to all feedback, and I apologize if I
missed some feedback from you in the past.

If you have specific issues you'd like to raise, please file one bug per
issue in the W3C bug tracker (product "HTML WG", component "The srcset



I've replied to some of your specific points below. I didn't get to all
of them, but I think some of the other emails on this thread have
covered things pretty well. If there's a specific issue which I've
omitted below that you'd like to discuss, please call my attention to

> The espoused goal of allowing the user agent to have the option to
> override the authors declarations is not supported in the srcset
> specification design.

On the contrary, step 17 of the "process the image candidates" algorithm
allows the UA to choose whichever candidate it prefers.


> "3.5 Relative units
> This section mentions use cases that occur post-layout and in
> order for the UA to solved technical challenges such as choosing
> a sharp image it needs to know the images sizes.  To choose the
> lowest or highest resolution images the UA would need to know the
> relationship between them.  The srcset design specification fails
> to supply this information to the UA.

If the UA wants to choose the highest resolution image, it can simply
choose the candidate with the highest associated pixel density. I might
be misunderstanding your point though.

> "4 Requirements
> I would note that this requirment includes making changes to the
> images post-layout. The srcset hints are designed for pre-layout
> selection when the actual required images size is unknown. Once the
> layout is computed the UA could better use information about the
> actual image sizes to select an appropriate images but the srcset
> design fails to support this information.

One of the design constraints of srcset="" is that it be possible for
the UA to choose the appropriate image candidate while prefetching, so
asset choice cannot rely on layout information.

>  "10. The solution SHOULD afford user agents with the ability to
>  provide a user-settable preference for controlling which source
>  of an image they prefer[…]"

I don't think either specification should mandate browser UI. That said,
both proposals are compatible with such a browser setting, should a UA
choose to implement one.

> The srcset proposal is inconsistent with the design goals for the
> srcset and picture specifications of using the picture element for
> art-direction and the srcset for only resolution choice.

The srcset="" specification does not purport to meet such a design goal.

> There is no mention in the srcset specification that the
> author must only use it to supply the same image at different
> resolutions.

This is intentional, because the srcset="" specification aims to solve
both the HiDPI case and the art direction case.

Received on Tuesday, 5 February 2013 23:17:28 UTC

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