  Quantum fields are generally taken to be operator-valued distributions,
linear functionals of test functions into an algebra of operators; here the
effective dynamics of an interacting quantum field is taken to be nonlinearly
modified by properties of test functions, in a way that preserves Poincar\'e
invariance, microcausality, and the Fock-Hilbert space structure of the free
field. The construction can be taken to be a physically comprehensible
regularization because we can introduce a sequence that has a limit that is a
conventional interacting quantum field, with the usual informal dependence of
the effective dynamics on properties of the experimental apparatus made
formally explicit as a dependence on the test functions that are used to model
the experimental apparatus.
