What Is Appropriate Attire for a Graduation Ceremony?

Different universities have different degrees of pomp and circumstance in their graduation ceremonies, ranging from the US mega-school approach of, "Would all 10,000 graduates please stand? Thank you. You have just graduated from Mega-University," to walking across the stage single file and shaking the hand of some dignitary, to ceremonies like the ones we have at The University of Western Ontario, which involve kneeling before the chancelor or a pro-chancelor (we do undergrads in threes) and being admitted to the degree. My role in these ceremonies, Esquire Bedel (ceremonial mace carrier), is depicted below.

I have been to many different ceremonies, but I have never seen a university impose a dress code on the graduates. Understandably Cambridge took some flak when they tried to ban kilts:

CAMBRIDGE University last night showed signs of backing down after banning students from wearing kilts to their graduation ceremonies.
The English university told male students they must only wear formal dress of a black morning suit and white bow tie. But the interdict sparked fury among patriotic Scottish students, and the university has been inundated with e-mails from angry alumni demanding that the dress law be removed. Yesterday, officials at the university admitted they were prepared to make exceptions for those who felt strongly about wearing their national dress.

[h/t to BF for the pointer]