  Low-valence nickelates $-$ including infinite-layer (IL) and trilayer (TL)
compounds $-$ are longstanding candidates for mimicking the high-temperature
superconductivity of cuprates. A recent breakthrough in the field came with the
discovery of superconductivity in hole-doped IL nickelates. Yet, the degree of
similarity between low-valence nickelates and cuprates is the subject of a
profound debate for which soft x-ray spectroscopy experiments at the Ni $L$-
and O $K$-edge provided critical input. In this review, we will discuss the
essential elements of the electronic structure of low-valance nickelates
revealed by x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray
scattering (RIXS). Furthermore, we will review magnetic excitations observed in
the RIXS spectra of IL and TL nickelates, which exhibit characteristics that
are partly reminiscent of those of cuprates.
