Observed wavelength of Mg_II and C_III spectroscopic lines as a function of redshift. The horizontal dashed line shows the observed wavelength of a single detected optical spectral line in source R446. The vertical lines indicate the reported specz (orange), photoz (green), and XZ (blue). The dotted vertical lines show the errors of photoz and XZ, respectively. The specz was derived assuming Mg_II, but agrees with XZ and photoz if we assume C_III instead.