The Highway Code is a common set of guidelines for use by all road users, it's purpose is to take the guesswork out of the situations described above. How on earth is somebody supposed to know what you are trying to convey with your lights if everybody has a different way of using them? For example, just from previous replies, if somebody were to turn on their indicators would you think they were asking you to overtake, trying to thank you or maybe they were indicating their intention to change direction?
As for different headlight flashes having different meanings, I've never heard such nonsense!
And another thing, drivers who insist on flashing their headlights at you at night - don't even get me started!!