sdd:primitive
sdd:primitive selects which primitive a sdd:Datum renders as. Its objects are the primitive individuals of the frozen leaf layer (spec §4.5) — sdd:text and sdd:number in this slice, with link, image, color, sdd:vector, and rich arriving in later plans.
A data line has the shape primitive path? value?: sdd:primitive is always present on a Datum, while sdd:binds and sdd:value are present only when the datum is grounded. Because every rendered value in a node is a Datum instance rather than a bare literal, sdd:primitive is what tells a renderer which drawing rule to apply without inspecting the value itself.