The ElementTiming API will allow developers to know when certain important text elements are first displayed on the screen. It will also enable analytics providers to measure the display time of text that takes up a large fraction of the viewport when they first show up.
Developers should be informed of the time at which key elements of their website are first rendered. Usually this means images and/or text. Text is important for news websites, articles of online encyclopedias, email providers, etc. First contentful paint is insufficient because it is triggered with almost any element.
Docs: https://docs.google.com/document/d/10Tx-NgEnmtDMXxrcWrKpIu6g0JwItiumrI8shC58qKw/edit#
Explainers: https://docs.google.com/document/d/1xhPJnXf0Nqsi8cBFrlzBuHavirOVZBd8TqdD_OyrDGw/edit?usp=sharing