This specification defines a set of CSP-like directives that de-prioritize the loading of resources that negatively impact the user experience of a web application. These author-imposed "interventions" can help improve the loading performance of an application's primary content by deferring (or outright stopping!) the loading of first or third-party content that would otherwise harm the user experience (e.g., a web-font that takes too long to load).
Conforming user agents modify their behavior to enforce these directives, and ignore "slow path" resources or behaviors. Web Applications that embed external documents, or link to them, can use these directives as guarantees that prevent degradation of user experience: in effect, if a non-critical resource is adversely affecting the user experience, the user agent can ignore, de-prioritize, or defer it (depending on the directive).
The primary aim of the directives defined in this specification is to target performance anti-patterns caused by first or third-party resources: that is, where those resources are not in control of the application's author, but there is a risk that those resources could negatively affect the user experience of the application in a way the author cannot directly control. Deploying directives that guarantee performance aspects could serve as a signal to increase a site's ranking in search engines - as well as serve as a signal to users that the site won't unnecessarily sacrifice the user experience. Furthermore, content blockers could use those guarantees in order to make their decision whether to automatically block a certain resource or not.
I tried to rewrite it a bit...
This specification defines a set of CSP-like directives that de-prioritize the loading of resources that negatively impact the user experience of a web application. These author-imposed "interventions" can help improve the loading performance of an application's primary content by deferring (or outright stopping!) the loading of first or third-party content that would otherwise harm the user experience (e.g., a web-font that takes too long to load).
Conforming user agents modify their behavior to enforce these directives, and ignore "slow path" resources or behaviors. Web Applications that embed external documents, or link to them, can use these directives as guarantees that prevent degradation of user experience: in effect, if a non-critical resource is adversely affecting the user experience, the user agent can ignore, de-prioritize, or defer it (depending on the directive).
The primary aim of the directives defined in this specification is to target performance anti-patterns caused by first or third-party resources: that is, where those resources are not in control of the application's author, but there is a risk that those resources could negatively affect the user experience of the application in a way the author cannot directly control. Deploying directives that guarantee performance aspects could serve as a signal to increase a site's ranking in search engines - as well as serve as a signal to users that the site won't unnecessarily sacrifice the user experience. Furthermore, content blockers could use those guarantees in order to make their decision whether to automatically block a certain resource or not.