XMM-Newton RGS spectra of Mrk 110, fluxed against a Γ = 2 power-law, showing the 2004, 2019d, and 2020 observations spanning the typical flux range of the AGN. The expected wavelength of the O VII forbidden line (22.1 Å) is shown by the dotted vertical line. Strong and broad O VII emission is seen in the brightest 2004 observation, which diminishes towards the 2019d and 2020 (faintest) observations. The continuum also becomes somewhat softer with increasing flux. The spectra are re-binned to Δλ = 0.2 Å bins for clarity.