Automatic Quality Render settings

Could we get some information on what the "Automatic" Quality Render setting does with file quality? Looking up the Manual (pg 3511), it doesn't have any particular information other than "Quality: If the currently selected option in the Render to drop-down menu has options for changing the compression quality, this drop-down menu lets you choose the quality you want to use. Otherwise, it’s disabled."

Near as I can tell, it's a Constant Quality option that will set the bitrate to meet the desired setting.

As a guide, I find Best to be comparable to x264 at CQ 16. (Which is damn good!)