requestAnimationFrame: what exactly is the timestamp?

Question

I have always thought that timestamp used by requestAnimationFrame is the same as usual timestamp in JavaScript, that is number of milliseconds since January 1st, 1970. Today I

Answer 1

Finally, I found the answer in an article by Paul Irish and the specification of High Resolution time:

requestAnimationFrame API: now with sub-millisecond precision

High Resolution Time

The rAF time is "measured relative to the start of navigation of the document", that is relative to the "navigationStart attribute of the PerformanceTiming interface".