[Proposal] Priority hints policy

[Malvoz]

The Priority Hints API gives developers the ability to signal to browsers the priority in which resources ought to be downloaded. Having a parametric policy would simplify implementation and could itself act as a priority signal.

Although parameterized features help provide further control - not providing granular enough control is concerning as developers would only be able to set priorities based on browsing contexts and not per content-type or preferably per resource:
Feature-Policy: importance 'self'(high) - indicating all resources from the site to be of high priority.

The above is somewhat salvageable by either having the importance policy separated into multiple policy names:
image-importance, script-importance, frame-importance etc. - which probably doesn't win over any fans, or if parametric policies would allow for e.g: importance 'self'(style: high; frame: low; img: auto);

This type of fine grained control is obviously a question for the issue about parameterized features (w3c/webappsec-permissions-policy#163).

But unless parametric policies are able to effectively target a specific resource, e.g. element #id's (seems like a security issue to me if applicable to some other policies), a policy wouldn't help developers accomplish what priority hints intend to do - which is fine grained control per-resource basis.

With that said, I think priority hints as a policy should at least be considered.