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

MDN says:

The callback has one single argument, a DOMHighResTimeStamp, which indicates the current time (the time returned from performance.now() )

And this is what performance.now() returns:

The returned value represents the time elapsed since the time origin.

The time origin is a standard time which is considered to be the beginning of the current document's lifetime.