Something about the rules on edwardian times:
Full Court Dress
: low bodice, short sleeves, and train to dress not less than three yards in length from the shoulders. Whether the train is cut round or square is a matter of inclination or fashion. The width at the end should be 54 inches. It is also imperative that a presentation dress should be white if the person presented be an unmarried lady and it is also the fashion for married ladies to wear white on their presentation unless their age rendered their doing so unsuitable The white dresses worn by either debutante or married ladies may be trimmed with either colored or white flowers according to individual taste.
High Court Dress
: dress of silk satin or velvet may be worn at Their Majesties Courts and on other State occasions by ladies to whom from illness infirmity or advancing age the present low Court dress is inappropriate. Bodices in front cut square or heart shaped which may be filled in with white only either transparent or lined at the back high or cut down three quarters height. Sleeves to elbow either thick or transparent. Trains, gloves, and feathers as usual. It is necessary for ladies who wish to appear in High Court Dress to obtain Royal permission through the Lord Chamberlain. This regulation does not apply to ladies who have already received permission to wear high dress. [...]
from Edwardian Promenade » 2007 » December