A strange phrase found in Chaucer's Miller's Tale used of a pair of shoes worn by a dandyish clerk. The upper parts of these fancy shoes were cut away, somewhat like tracery, allowing the red hose to show through. The reference is to a *rosace in the old St Paul's Cathedral. The Latin phrase for these shoes was calcei fenestrati, i.e. window shoes.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.