The screenshot in the M3 Beta announcement shows buttons in the navigation rail which feature icons above their text, but… how?
The Editor only offers right and left as icon placement options.
Would like to see above and below icon placement options added for both Normal buttons and Menubuttons.
I see now that what I mistook for buttons in the navigation rail are actually instances of the new NavigationLinks. These are nice!
(I would still like to be able to be able to place icons above or below text in buttons though. 
)
Is the navigation rail intended to be populated solely by NavigationLinks?
(When I placed normal buttons there, the left and right edges were cut off – and adjusting their margins had no effect.)