Read the full story https://www.w3.org/blog/news/archives/6203?pk_campaign=feed&pk_kwd=w3c-invites-implementations-of-page-visibility-level-2-2
The Web Performance Working Group invites implementation of the Candidate Recommendation of Page Visibility Level 2. This specification defines a means to programmatically determine the visibility state of a document. This can aid in the development of resource efficient web applications.