Time-series of UV-wavelength spectroscopy of SN 2011iv obtained with Swift (purple) and HST (blue) over the course of nearly a month beginning 5 d before maximum brightness. Smoothed versions of the Swift spectra are presented in black. The insets are close-up views of the wavelength ranges 1700–3000 (left) and 2900–3900 (right), comparing the 0 d spectrum of SN 2011iv to the 0 d spectra of SN 2011fe (pink; Mazzali et al. 2014) and SN 2013dy (green; Pan et al. 2015). The light-blue vertical areas mark the regions f_λ (2770) and f_λ (2900), which define the UV ratio (see Appendix A). The green and blue shaded regions indicate the area enclosed by the pseudo-equivalent widths defined as pW01 and pW02, respectively (Sect. 5.1.2).