The NavigationInfo node defines this information in a a nonambiguous way, so that the world's creator can be assured of a consistent user experience. In order to understand how it works, it's important to understand the event model for VRML 2.0. Events are actions that can be performed upon a node in a VRML world, or can be generated by a node in that world. One way to think about the VRML 2.0 event model is as a series of components that get wired together to create a virtual machine. As with the logic of electronic circuits, you can only wire outputs to inputs.
Sensors are triggers that fire off a message in response to some activity.
TimeSensor acts like a ticking clock, firing off events at regular intervals, or as an alarm clock, ringing at a specific point in time. If the sensor has been wired to an eventIn of another node, that node receives the message. SphereProximitySensor works like its counterpart, but the region defined is spherical. Thus a script can send messages to nodes inside a VRML world and can receive messages from them. VRML 2.0 will be in widespread release by midsummer, and you can expect that the two browser heavies, Netscape and Microsoft, will incorporate it into their browsers.