Don't know how much it matters to you guys, but most of what passes for heraldry these days, including the descriptions of the various elements, are not medieval but 16th - 18th century meanings. Heraldry was not an exact science in the middle ages, and there was pretty much no regulation of it for nearly the entire medieval period. Until some time in the 14th century the most common way of acquiring arms was simply to invent them for yourself. It wasn't until 1415 that any official organization existed to regulate them and settle disputes. So if you portay a knight from before then, they sky's really the limit, within reason, and what we know about trends of heraldic design throughout history.