WPT details: WPTs will be added as a part of the implementation
This proposal is to add an event that would fire on a content-visibility: auto element when the rendering state of the element changes due to any of the attributes that make the element relevant to the user (https://www.w3.org/TR/css-contain-2/#relevant-to-the-user)
The use-case for this is to let developers have greater control over when to stop or start rendering in response to the user-agent stopping or starting rendering of the content-visibility subtree. For example, the developer may want to stop React updates in a subtree that is not rendered by the user-agent. Similarly, the developer may want to stop any other script updates (e.g. canvas updates) when the user-agent is not rendering the element.
Docs: https://github.com/vmpstr/web-proposals/blob/main/explainers/cv-auto-event.md
Explainers: https://github.com/vmpstr/web-proposals/blob/main/explainers/cv-auto-event.md