Please answer a question about the following article about Gothic architecture:

Other cities with a concentration of secular Gothic include Bruges and Siena. Most surviving small secular buildings are relatively plain and straightforward; most windows are flat-topped with mullions, with pointed arches and vaulted ceilings often only found at a few focal points. The country-houses of the nobility were slow to abandon the appearance of being a castle, even in parts of Europe, like England, where defence had ceased to be a real concern. The living and working parts of many monastic buildings survive, for example at Mont Saint-Michel.

What style are most windows on secular Gothic structures?
flat-topped with mullions