/usr is shareable, static.

Required	bin	Most user commands
	include	C header files
	lib	Libraries
	sbin	Non-essential system binaries
	local	Host-specific
	share	Architecute-independent
Specific Options	X11R6	XWindow System
	games	Games and educational binaries
	lib*	Alternate format libraries
	src	Source code

X11R6 is granted a historical exception.