A quote from RFC 791 document "Fragmentation, transmission and reassembly across a local network which is invisible to the internet protocol module is called intranet fragmentation and may be used."
A quote from easytechjunkie site "An Internet protocol (IP) module is a component that allows a non-networked device to connect to a network system."
How a local network, called intranet can be invisible to the Internet Protocol module if the Internet Protocol module allows a non-networked device connect to a network system?
As I see, a local network cannot be created if IP module can't see the intranet. But I don't think that RFC Document can contain false information. So I confused and don't know how to understand this strange situation.