  Nuclear magnetic resonance (NMR) shifts, if stripped off their uncertainties,
must hold key information about the electronic fluid in the cuprates. The early
shift interpretation that favored a single-fluid scenario will be reviewed, as
well as recent experiments that reported its failure. Thereafter, based on
literature shift data for planar Cu a contrasting shift phenomenology for
cuprate superconductors is developed, which is very different from the early
view while being in agreement with all published data. For example, it will be
shown that the hitherto used hyperfine scenario is inadequate as a large
isotropic shift component is discovered. Furthermore, the changes of the
temperature dependences of the shifts above and below the superconducting
transitions temperature proceed according to a few rules that were not
discussed before. It appears that there can be substantial spin shift at the
lowest temperature if the magnetic field lies in the CuO$_2$ plane, which
points to a localization of spin in the $3d(x^2-y^2)$ orbital. A simple model
is presented based on the most fundamental findings. The analysis must have new
consequences for theory of the cuprates.
