[Brian_K_White]

Those are user controls, to allow the user on one end to decide what to put into the container, and there are others to allow the user at the other side to decide what to take out of the container, not limits of the container.

The comment I'm replying to suggested that since one use case results in metadata that is meaningless or mis-matched between sender and receiver, the format itself should not even have the ability to record that metadata.