Position–velocity diagrams of selected H₂, H I, He I, [Kr III], [Se IV], [Fe II], and [Fe III] lines for M 1-11 (far left), Vy 2-2 (middle left), Hen 2-459 McD (middle right), and Hen 2-459 LDT (far right) observations. The H₂ 1–0 S(1) line from the top is overplotted over all the other lines as blue contours to facilitate direct comparison of the emission from H₂ and other species. The x-axis shows the velocity in kilometers per second relative to the nebular center, and the y-axis shows the spatial position along the slit with the orientation shown in Figure 1. Note that the H₂ 3-2 S(2) line is ∼50 km s⁻¹ redward of the position of the undetected [Se IV] line in the M 1-11 PV diagram.