Intent to Extend Origin Trial: Priority Hints
Yoav Weiss
Contact emails
domfa...@gmail.com, yo...@yoav.ws, kenji...@chromium.org
Spec
WICG spec: https://github.com/WICG/priority-hints
HTML Standard issue for discussion: https://github.com/whatwg/html/issues/3670
Summary
The intention of the Priority Hints API is to let developers signal to the browser how much a resource-fetching HTML element matters to the user experience. The browser may take this signal into consideration when prioritizing the request.
Link to “Intent to Implement” blink-dev discussion
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/65lfM2f0eeM
Goals for experimentation
The goal is to test potential resource loading speed-ups with Priority Hints, primarily by the use of:
<img src=... alt=... importance=high>, to allow developers to explicitly prioritize in-viewport images as high
<link rel=preload as=... importance=low>, to allow developers to down-prioritize certain preloads which may contend with other more important resources needed immediately
<script src=... async importance=high>, to allow developers to prioritize important but non-parser-blocking scripts.
Potential <iframe> testing with other partners (for advertisements)
Though it should be noted that the effect of Priority Hints on an <iframe>’s subresources has not been decided upon yet, so no immediate testing could be done with this
The metrics used to measure potential resource loading speed-ups will be measured by partners using Priority Hints during the trial period. Given some recent studies in HTTP/2 prioritization on the server-side, one of our goals is to pair up with vendors that might enable us to test Priority Hints with a hosting provider that handles HTTP/2 priorities well, to see the full effects.
Experimental timeline
M75-M76.
Any risks when the experiment finishes?
There are no risks, as the only markup change required to use the feature is an HTML content attribute which will be ignored by browsers that do not support Priority Hints. The worst thing that could happen here is any potential speed-ups Priority Hints provides would go away in the gap between the experimentation deadline, and shipping.
Reason this experiment is being extended
Enable our partners to gather more data on the benefits, and enable some of them (who lagged behind their initial commitments) to start experimenting.Ongoing technical constraints
No.
Debuggability
Same as in I2I.
Will this feature be supported on all five Blink platforms supported by Origin Trials (Windows, Mac, Linux, Chrome OS, and Android)?
Yes.
Link to entry on the feature dashboard
