Even how courtiers walked into a room was dictated by etiquette. Who was allowed to enter a room first depended on your position. First were the princes, then officers of the Court and then courtiers. Imagine the scandal if a courtier walked in first! The pages or ushers would open both of the tall double doors for someone holding the rank of a prince but only one was opened for lesser dignitaries.
And if you were a nobleman or woman you were not allowed to open a door yourself! You had to wait until an usher came along - no matter how long that might take.