Comparison of the primary and secondary spectral classification criteria (x and y axis, respectively). The shaded areas indicate the regions where the two criteria agree on the spectral type. If these are not in agreement, the classification depends on the FWHM of C ivλ5801−12 Å. This is only the case for DR1, which we assign the spectral type WO3, in agreement with previous classifications. The dashed shaded region indicates where the WC sequence begins.