Classic Mac OS window headers had striped or dot patterns that were kind of similar to rugged parts of various physical tool handles. So they were both decorati

Classic Mac OS window headers had striped or dot patterns that were kind of similar to rugged parts of various physical tool handles. So they were both decorative in a way and informational: this is a part you can hold and drag around. A typical interface will have a lot of such parts that are both functional and decorative, so it will feel just right. Purely decorative parts are also possible (and even desirable), but they should be personal. A set of colors chosen by the user, a background texture, a picture that the user keeps on the desktop and so on.