SoVRMLProximitySensor(3) on Linux
The text 5a51166691b1, as Debian 8 (Jessie) shipped it.
The SoVRMLProximitySensor class is used to generate events when the viewer enters or exits a region. The detailed class documentation is taken verbatim from the VRML97 standard (ISO/IEC 14772-1:1997). It is copyright The Web3D Consortium, and is used by permission of the Consortium: