Using the book: an introduction | Using the medieval book | Khan Academy

More extensive notes were sometimes written on tiny paper or parchment slips like the one seen here. Students are known to have used them to take down notes in the classroom or when they were studying a text at home. Few of them survive today. Not only were they easy to lose, but many of them were actually thrown out, similar to the fate of our modern day “sticky notes.” In some manuscripts they survive because they were tucked in between the pages, as seen here.
https://www.khanacademy.org/humanities/medieval-world/medieval-book/using-medieval-book/a/using-the-book-an-introduction