  This paper describes a modular framework for the description of electroweak
scattering and decay processes, including but not limited to Z-resonance
physics. The framework consistently combines a complex-pole expansion near a
s-channel resonance with a regular fixed-order perturbative description away
from the resonance, in a manifestly gauge-invariant scheme. Leading vertex
correction contributions are encapsulated in form factors that can be predicted
or treated as numerical fit parameters.
  This framework has been implemented in the publicly available object-oriented
C++ library GRIFFIN. Version 1.0 of this library provides Standard Model
predictions for the process $f\bar{f} \to f'\bar{f}'$ with full NNLO and
leading higher-order contributions on the Z-resonance, and with NLO corrections
off resonance. The library can straightforwardly be extended to include
higher-order corrections, should they become available, or predictions for new
physics models. It can be interfaced with Monte-Carlo programs to account for
QED and QCD initial-state and final-state radiation.
