  Decays of neutral D-mesons are considered phenomenologically without invoking
any particular models. Special attention is given to cascade decays with
intermediate neutral kaons where coherent double-flavor oscillations (CDFO)
become possible. We show necessity and unique possibilities of experiments on
CDFO. They allow to relate with each other widths and masses of D-meson
eigenstates, to separate interference effects due to $D^0 - \bar D^0$ mixing
and/or Cabibbo-favored vs. doubly-suppressed transitions. Such experiments
provide the only known ways to unambiguous model-independent measurements of
all CP-violating parameters and of Cabibbo-doubly-suppressed amplitudes, where
the New Physics may have more prominent manifestations. Similar experiments
would be useful and interesting also for charged $D$-meson decays to neutral
kaons.
