Chang-ao (Chinese: 長襖) is the historical Chinese attire for women. It is a form of formal wear, and is often perceived as a longer version of ruqun. However, it was actually developed from zhiduo during the Ming Dynasty, and is worn over a skirt. It is wide-sleeved, shorter than zhiduo and has no side panels (暗擺) at the side slits (thus showing the skirt worn underneath). There is often an optional detachable protective huling (護領, lit. "protect collar") sewn to the collar. The huling can be of white or any other dark colours. The collar is of the same colour as the clothing.