"ResourceTiming exposes accurate performance metrics for all of the resources fetched on your page. You can use this data for a variety of scenarios, from investigating the performance of your third-party libraries to taking specific actions when resources aren’t performing according to your performance goals."

JavaScript Loading Priorities in Chrome

"The new HTML5 elements can offer so much to improve user experience and provide consistency and accessibility ‘out of the box’ to save developers time. But […] the concepts are currently let down by sloppy, or absent support from the browser and assistive technology manufacturers."