  The first step of any QFT calculation, aiming at phenomenological
predictions, is the matching of the theory to Nature. The matching procedure
fixes the parameters of the theory in terms of an equal number of external
inputs that, if the theory is expected to reproduce observations, must be
experimentally measured physical quantities. At the sub-percent level of
accuracy QED radiative corrections become important and the theory expected to
describe the hadronic Universe is QCD+QED. Phenomenological predictions
deriving from lattice QCD calculations do depend, at this level of precision,
upon the choice of the external inputs used to match/define the approximate
theory. In this written version of my talk I concentrate on the theoretical
aspects of the matching procedure of lattice QCD$+$QED and of the definition of
QCD, strongly advocating a community agreement on the matching scheme to be
used in future lattice QCD calculations.
