  We present a detailed overview of the physics of two-color soliton molecules
in nonlinear waveguides, i.e. bound states of localized optical pulses which
are held together due to an incoherent interaction mechanism. The mutual
confinement, or trapping, of the subpulses, which leads to a stable propagation
of the pulse compound, is enabled by the nonlinear Kerr effect. Special
attention is paid to the description of the binding mechanism in terms of
attractive potential wells, induced by the refractive index changes of the
subpulses, exerted on one another through cross-phase modulation. Specifically,
we discuss nonlinear-photonics meta atoms, given by pulse compounds consisting
of a strong trapping pulse and a weak trapped pulse, for which trapped states
of low intensity are determined by a Schr\"odinger-type eigenproblem. We
discuss the rich dynamical behavior of such meta-atoms, demonstrating that an
increase of the group-velocity mismatch of both subpulses leads to an
ionization-like trapping-to-escape transition. We further demonstrate that if
both constituent pulses are of similar amplitude, molecule-like bound-states
are formed. We show that z-periodic amplitude variations permit a coupling of
these pulse compound to dispersive waves, resulting in the resonant emission of
Kushi-comb-like multi-frequency radiation.
