  We propose a framework for high-energy interactions in which resonance decays
and electroweak branching processes are interleaved with the QCD evolution in a
single common sequence of decreasing resolution scales. The interleaved
treatment of resonance decays allows for a new treatment of finite-width
effects in parton showers. At scales above their offshellness, resonances
participate explicitly as incoming and outgoing states in branching processes,
while they are effectively "integrated out" of the description at lower scales.
We implement this formalism, together with a full set of antenna functions for
branching processes involving electroweak (W/Z/H) bosons in the Vincia shower
module in Pythia 8.3, and study some of the consequences.
