Scrolls were gradually replaced by concertina binding (經摺裝) from the Tang period onward. The advantage was that it was now possible to flip to a reference without unfolding the entire document. The next development known as whirlwind binding ("xuanfeng zhuang" 旋風裝) was to secure the first and last leaves to a single large sheet, so that the book could be opened like an accordion. Around the year 1000, butterfly binding was developed. Woodblock prints allowed two mirror images to be easily replicated on a single sheet. Thus two pages were printed on a sheet, which was then folded inwards. The sheets were then pasted together at the fold to make a codex with alternate openings of printed and blank pairs of pages. In the 14th century the folding was reversed outwards to give continuous printed pages, each backed by a blank hidden page. Later the sewn bindings were preferred rather than pasted bindings. Only relatively small volumes ("juan 卷") were bound up, and several of these would be enclosed in a cover called a "tao", with wooden boards at front and back, and loops and pegs to close up the book when not in use. For example, one complete Tripitaka had over 6,400 "juan" in 595 "tao". Despite the productive effect of woodblock printing, historian Endymion Wilkinson notes that it never supplanted handwritten manuscripts. Indeed, manuscripts remained dominant until the very end of Imperial China:  Not only did manuscripts remain competitive with imprints, they were even "preferred" by elite scholars and collectors. The age of printing gave the act of copying by hand a new dimension of cultural reverence. Those who considered themselves real scholars and true connoisseurs of the book did not consider imprints to be real books. Under the elitist attitudes of the time, "printed books were for those who did not truly care about books." However, copyists and manuscript only continued to remain competitive with printed editions by dramatically reducing their price. According to the Ming dynasty author Hu Yinglin, "if no printed edition were available on the market, the hand-copied manuscript of a book would cost ten times as much as the printed work," also "once a printed edition appeared, the transcribed copy could no longer be sold and would be discarded." The result is that despite the mutual co-existence of hand-copied manuscripts and printed texts, the cost of the book had declined by about 90 percent by the end of the 16th century.