  The form of the kernel that controls the dynamics of the Bethe-Salpeter
equations is essential for obtaining quantitatively accurate predictions for
the observable properties of hadrons. In the present work we briefly review the
basic physical concepts and field-theoretic techniques employed in a
first-principle derivation of a universal (process-independent) component of
this kernel. This "top-down" approach combines nonperturbative ingredients
obtained from lattice simulations and Dyson-Schwinger equations, and furnishes
a renormalization-group invariant quark-gluon interaction strength, which is in
excellent agreement with the corresponding quantity obtained from a systematic
"bottom-up" treatment, where bound-state data are fitted within a well-defined
truncation scheme.
