Well, that was a waste of 2 hours of my life trying to figure it out by digging in code. Next time, please take longer to answer so I don't feel like I wasted so much of my time.
FWIW, the way I'd find this (or if I actually checked properly rather than just trying to recall from memory) is I'd search the js/core directory for "XF.Overlay" and specifically the click handler function.
The "options" object at the top of each click/element handler pretty much tells you what can be passed in via data attributes:
cache: true is the same as data-cache="true" and forceFlashMessage: false is the same as data-force-flash-message="off" etc.