Level 1/3: Structural Verilog : Structural, Heirarchic, Netlist
module subcircuit(clk, rst, q2);
INPUT clk, rst;
OUTPUT q2;
DFFR Ff_1(clk, rst, a, q1, qb1),
Ff_2(clk, rst, q1, q2, qb2),
Ff_3(clk, rst, q2, q3, qb3);
NOR2 Nor2_1(a, q2, q3);
endmodule
Just a netlist.
There are no assignment statements that transfer data between registers in structural RTL (but it's still a form or RTL).