Document complete before start render.

Please look at these test results:

Start Render time is: 0.465s
Document complete time is: 0.396s

How can a document being complete before rendering is started?

The browser UI is painted on the main thread and almost in an idle loop. For a really fast page it’s not uncommon for the onLoad to fire when the browser has finished processing the DOM and doing the layout internally but before the screen actually gets painted.