This is an interesting point. Taken to its extreme, Postel's law will trade some abstraction for robustness. Conversely, Hyrum's law will trade some robustness for abstraction.
Postel's law has turned out to be a disaster for security, and for extensibility. If everything you can get already means something, nothing can ever mean anything new.
"Be clear about what you will accept", instead. And, make sure there is an easy way to discover why it was not accepted.
