It is proper right-handed. The rotation matrix for a right-handed rotation about the z-axis with a rotation angle psi is given by
Rz(psi) = [ cos(psi) sin(psi) 0;
-sin(psi) cos(psi) 0;
0 0 1]
For a rotation angle of 90 deg (pi/2) this results in
angle2dcm(pi/2,0,0,'zyx')
ans =
0.0000 1.0000 0
-1.0000 0.0000 0
0 0 1.0000
As an example, the vetor v in the graph below has coordinates [1; 0; 0] in the un-primed reference frame (left). When rotating the reference frame about 90 deg (right-handed) about the z-axis the vector points in negative y direction, [0; -1: 0], which corresponds to the result from the matrix-vector multiplication:
angle2dcm(pi/2,0,0,'zyx')*[1; 0; 0]
ans =
0.0000
-1.0000
0
