Casing refers to the decorative trim that surrounds doors and windows. It not only enhances the appearance of the opening but also helps to hide any gaps between the jamb and the wall. Casing plays a crucial role in ensuring that doors and windows are properly aligned and function smoothly. There are various designs of casing available, ranging from simple and plain to ornate and elaborate. Examples of simple designs include clamshell and square-edge casing, while colonial and Victorian casing are more intricate. Pre-hung doors often come with casing on one side, with the need to add trim to the other side. When replacing doors, it is necessary to remove the existing casings and install new ones. The installation process for casing on both doors and windows requires accurate measurements and right angles.