What does the first '1' signify in the 14th line (SimModel = feedback(sys,1,4,2,1);) ? the general syntax for feedback is (sys1,sys2​,feedin,fe​edout). How does the matlab take when i introduce a '1' as sys2 in this case?

clc;clear;

A = [1.1269 -0.4940 0.1129, 1.0000 0 0, 0 1.0000 0];

B = [-0.3832 0.5919 0.5191];

C = [1 0 0];

D = 0;

Plant = ss(A,[B B],C,0,-1,'inputname',{'u' 'w'},'outputname','y'); Q=2.3; R=1; [kalmf,L,~,M,Z] = kalman(Plant,Q,R); kalmf = kalmf(1,:); a = A; b = [B B 0*B]; c = [C;C]; d = [0 0 0;0 0 1]; P = ss(a,b,c,d,-1,'inputname',{'u' 'w' 'v'},'outputname',{'y' 'yv'}); sys = parallel(P,kalmf,1,1,[],[]); SimModel = feedback(sys,1,4,2,1);