Which sentence contains a restrictive clause?

one thousand and one nights, also known as arabian nights is a collection of stories whose basic structure is that of embedded narrative. this technique refers to a main story which works as the common frame - or framing narrative - for the other stories, and then this series of stories which are connected to the main one. this technique can also be referred to as a story within a story. the stories stem from the original tale, some begin and end on their own, some are connected to the previous or following one, by means of questions that are answered in the subsequent tale, or characters which reappear.

"it's more of an essay than story, but perhaps it is best described as a mood-piece: it uses a lot of musical imagery, not to mention sea imagery, religious imagery, and any other imagery that suits his purpose."