Aman in black walks along on the road, a truck turns the corner and stops to a screeching halt, how did the truck driver see the man dressed in black?

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.