The Composer is a machine added by RFTools. It combines multiple Shape Cards into a single Shape Card. Shape Cards are combined from top to bottom. There are three modes the Composer can use:
Addition (+): Adds non-intersecting parts together.
Substraction (-): Removes intersecting parts. Acts diametrically opposite to Intersect.
Intersect (^). All non-intersecting parts are removed. Acts diametrically opposite to Subtraction.
The first card is always the base shape in addition mode. The bottom-most slot is the output slot and requires a Shape Card to be entered. Replacing the Shape Card in the bottom-most slot makes another card of the current setup.