Desk features are items that are commonly found on desks, such as inkwells, bells, rolltops, kneeholes, and inboxes. An inkwell is a container for holding ink, usually made of glass or ceramic, which was used to fill fountain pens before the invention of the ballpoint pen. A bell is a device that makes a ringing sound when it is struck, and was often used in offices to signal the end of the workday. A rolltop is a type of desk with a sliding top that can be rolled up to reveal a storage area underneath. A kneehole is an opening in the desk that allows the user to sit closer to the desk surface. An inbox is a tray or box used to store incoming documents and correspondence.