I have just been reading the "UI+Serious error" topic, and I am concerned about the regular use throughout the discussion of the word ILLEGAL.
Why it might be technically acceptable, the reason I rail against the word is because of the effect its use has on newcomers to the game or newcomers to Duplicate Bridge or newcomers to Tournament Bridge.
As soon as the accusation is made to someone that they have done something "illegal" then their interest in coming back to play more bridge decreases significantly, and the same goes for all those around them.
There are times when "illegal" is justifiable, but in UI situations it is very difficult for even the best players to make the right decisions and we need to find a way of saying that what they did needs rectification rather than (because of the inference people draw because of the regular use of the word "illegal") punishment.
It is up to us as a TD community to lead in the best use of language and in making newish bridge players comfortable. We can still apply the rules firmly but we need to minimise of use of certain words if we are to keep people playing the game.