isPrimitive property

Whether this occurrence is a primitive cell (gate, operator, register, etc.) whose internal structure is not useful for design navigation.

Set by the parser/adapter that creates the occurrence. The netlist adapter sets this for cells that lack a module definition in the JSON or whose definition starts with $ (netlist built-in primitives). Tool-specific primitives (e.g. ROHD's FlipFlop → $dff) are handled by the synthesizer mapping them to $-prefixed definitions before the JSON is written.