Fragments of older manuscripts can often be found in the covers of old books. Namely, for lack of book material, bookbinders would use parts of manuscript books that were considered anachronistic or obsolete at the time of the first printed books. Thus, when restoring the covers of books, we often come across handwritten fragments of parchment that served to amplify the ridge. Sometimes, such fragments can be merged into larger parts from which one can work out what kind of text and what period it is about (letter type). Also, in the absence of cover cardboard, bookbinders used glued sheets of printed texts from various books they had at hand. Thus, entire chapters of very rare books or unknown editions can be found.