Inactive, nonblocking assignment (NBA), and postponed regions

logic clk = 0, a = 0, b = 0;
always @(posedge clk) begin
  a <= 1;
  b <= a;
  #0 $display("D %0b %0b", a, b);
  $strobe("S %0b %0b", a, b);
end
initial #5 clk = 1;