Be liberal in what you accept, and conservative in what you send.
Be empathetic, flexible, and tolerant to any number of actions the user could possibly take.
This means accepting variable input from users, translating input to meet the requirements, defining boundaries for input, and providing clear feedback to the user.
Postel’s Law (also known as the Robustness Principle) was formulated by Jon Postel, an early pioneer of the Internet. The Law is a design guideline for software, specifically in regards to TCP and networks.