It is pretty prescriptive, but rings with hard-won wisdom. "He shall have no shirt upon him but a doublet of fustian lined with satin," it starts, which sounds pretty strict – but as anyone who has ever spent a day in armour will tell you, armoury chaffs in the same way cycling in a pair of jeans chaffs. The last thing you want under your armour (well, perhaps not the last thing – there are plenty of other things you would not want there, and plenty of people willing and able to put them there) would be buttons or extra seams, or anything that might ride up, or fall down.