  We construct several classes of hadronic matrix elements and relate them to
the low-energy constants in Chiral Perturbation Theory that describe the
electromagnetic effects in the semileptonic beta decay of the pion and the
kaon. We propose to calculate them using lattice QCD, and argue that such a
calculation will make an immediate impact to a number of interesting topics at
the precision frontier, including the outstanding anomalies in $|V_{us}|$ and
the top-row Cabibbo-Kobayashi-Maskawa matrix unitarity.
