Top panels refer to the line splitting diagrams (line strength vs. wavelength shift). The other panels show the comparison of the Stokes profiles computed using the PB-FS code (dashed lines) with the Zeeman-FS code (dotted lines). The two columns correspond to different field strengths, as indicated in the line splitting diagrams. The vertical dotted lines in the line splitting diagrams indicate the positions of the ⁷Li and ⁶Li D lines. The vertical dotted lines in the other panels correspond to the line center wavelength of the L = 0 → 1 → 0 transition in the reference isotope ⁷Li. The orientation of the magnetic field is given by (θ_B, ϕ_B) = (90°, 45°).