Before actually outputting any primitives, the application will want to specify the exact way in which the drawing appears on the display surface. This rendering process is controlled by output attributes. Output primitives have geometric and non-geometric attributes. Geometric attributes, such as the character height, affect the size and shape of a primitive, whereas non-geometric attributes are qualities such as colour, line style, etc.
Output attributes affect the appearance or rendering of primitives at the moment when the primitives are sent to GKS, and attributes are said to be bound to primitives at this time. Thus, modification of an attribute has no effect on primitives which have been output already. GKS attributes are said to be modal in character because, after setting an attribute, GKS is in a mode in which the value of that attribute will be bound to all primitives of the appropriate type which follow. Setting a different value for the attribute would then change the mode.