Robustness principle / postel’s law: “Be conservative in what you produce/output while being liberal in what you accept from others”1 Postel’s law is now considered harmful.
The Robustness Principle Reconsidered. Eric Allman. doi:10.1145/1978542.1978557 http://cacm.acm.org/magazines/2011/8/114933 -the-robustness-principle-reconsidered/fulltext
The Harmful Consequences of Postel’s Maxim https://tools.ietf.org/html/draft -thomson-postel-was-wrong-00