RAIL, an acronym for Response, Animation, Idle, and Load, is a performance model originated by the Google Chrome team in 2015, focused on user experience and performance within the browser. The performance mantra of RAIL is "Focus on the user; the end goal isn't to make your site perform fast on any specific device, it's to make users happy." There are 4 stages of interaction: page load, idle, response to input, and scrolling and animation. In acronym order, the main tenets are:...acknowledging any user input in 100ms or less. Animation When animating, render...JavaScript thread, work in chunks for less than 50ms to free up the thread...