Formline is a term first used by Bill Holm in his 1965 publication Northwest Coast Indian Art: An Analysis of Form to describe the primary distinguishing feature of the northern Northwest Coast two-dimensional design style. The formline is the curving line, which tends to swell and diminish throughout a composition, that creates the outline of the chosen subject. There are generally two formlines in a northern composition, known as the primary and the secondary formline. The primary formline is often black and the secondary formline is often red, although the two colors can be reversed. The stylistic elements created by formlines are u-shapes, ovoids, and s-shapes, among others. These elements consitute the negative space in a composition, which helps to define the positive space, or recognizable image.