It depends what you mean by discoverable: option+mouse action is a pretty standard macOS convention for alternate behavior and “double-click == drag all the way” isn’t unreasonable. The behavior of option+double-click is discoverable by simple composition of these features.

Also, most of this sort of functionality is documented in the built-in help system accessible through the help menu.

Perhaps more intuitively, you can also option+click on the green 'maximize' bubble to maximize the window.

(The option+mouse action is also a natural extension of the longstanding macOS convention that control+click == right click.)

I used macOS for about seven years before someone told me about this behavior. Never would've found it, otherwise.

I guess if I had been using it for twenty years I would've known about those old patterns you describe and would've thought to randomly try that key combination.

A tooltip at some point would've gone a long way. Pretty much an impossible feature to discover unless you're a toddler randomly pressing buttons or a greybeard that remembers OS 9

macOS user here since 2006. and i never knew about this or even thought to hold a button and click. you learn something new every day!

Apple Finder engineer here from 2000 - 2006 and would never have guessed about double-clicking or option-clicking window edges. This seems more like something I would have added to the Nautilus code in 1999.

+1

If only there was a website that could provide few relevant links to the “macos tips and tricks” query.