idea
The robustness principle postulates that outbound communication needs to be strict, and inbound communication needs to be flexible. It's called Postel's law after Jon Postel, who wrote the TCP spec:
Be conservative in what you do, be liberal in what you accept from others
This helps constructing robust systems by allowing some flexibility between the joints, while maximizing the chance that sent messages are understood.
One of the downside is potentially to accept erroneous messages and make errors silent, making them harder to spot.
links
references
- See Postel's law in Hacker's laws