You specify trapping in QuarkXPress in terms of the way an object color traps against a background color. Object color is the color applied to any item (like text or a box) that is in front of another color. Background color is the color applied to any item (like text or a box) that is behind an object color. When an object color and a background color meet on a printed page, the direction of the trap is determined by the relative luminance (lightness or brightness) of the colors.

An object color can be trapped to a background color in four ways:

• Overprint: When the object color prints directly on top of a background color.
• Knockout: When the object color cuts out (knocks out) its own exact shape from the background color.
• Spread: When the lighter object color is slightly enlarged so the object shape overlaps the darker background color.
• Choke: When the darker object color is slightly reduced so that the shape of the background color overlaps the object color

Trapping values in QuarkXPress are determined in one of three stages:

• Default trapping is the default method that QuarkXPress uses to automatically trap colors of varying hues and shades, based on the relative luminance of object and background colors. Use the Trapping pane of the Preferences dialog box (QuarkXPress/Edit > Preferences) to enter default trapping preferences for QuarkXPress and for individual QuarkXPress layouts (layout-specific trapping).
• Color-specific trapping is trapping that is specified for any object color relative to any background color. By specifying Overprint, Knockout, Auto Amount (+) for spreads, Auto Amount (–) for chokes, or Custom trap values in the Trap Specifications dialog box (Edit > Colors > Edit Trap), you can control the trapping relationships for every color in your Colors palette (Window menu).
• Item-specific trapping is trapping that is specified for any item using the Trap Information palette (Window menu).