- From: Tab Atkins Jr. <jackalmage@gmail.com>
- Date: Tue, 5 Nov 2013 11:15:06 -0800
- To: Simon Sapin <simon.sapin@exyr.org>
- Cc: public-web-perf@w3.org, www-style <www-style@w3.org>
On Tue, Nov 5, 2013 at 10:38 AM, Simon Sapin <simon.sapin@exyr.org> wrote: > Hi, > > (Please keep me in CC as I’m not subscribed to public-web-perf.) > > https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourcePriorities/Overview.html#resource-priorities-property > > In the current draft, the 'resource-priorities' CSS property applies to > content resources such as images in the <img> element. It shouldn’t. > > Because the 'postpone' value of that properties is a "must", this means that > the decision to fetch a resource is blocked on resolving the value of a CSS > property, which itself may depend on fetching external stylesheets. > > There are two issues with this: > > * This introduces a circular dependency. You don’t know when you’re supposed > to fetch a stylesheet until after you’ve applied it. > > * Some browsers speculatively parse HTML to find images and other resources > and start fetching them as soon as possible. CSS properties may not be > resolved yet at that point. Waiting for them introduces unnecessary delays. > > > To resolve both of these issues, I suggest changing the resource-priorities > property so that it does not apply to any "content resource" such as <img> > but only to "CSS resources" such as background-image. > > This change does not affect functionality since the property on content > resources is redundant with the attributes that this spec adds to various > HTML and SVG elements. Agreed. Browsers are *not* willing to give up their preload scanners, which adopting the property as currently specified would require. Content resources should be delayed with content attributes, which are preload-friendly. ~TJ
Received on Tuesday, 5 November 2013 19:15:53 UTC