  The observation of WW$\gamma$ production in proton-proton collisions at a
center-of-mass energy of 13 TeV with an integrated luminosity of 138 fb$^{-1}$
is presented. The observed (expected) significance is 5.6 (5.1) standard
deviations. Events are selected by requiring exactly two leptons (one electron
and one muon) of opposite charge, moderate missing transverse momentum, and a
photon. The measured fiducial cross section for WW$\gamma$ is 5.9 $\pm$ 0.8
(stat) $\pm$ 0.8 (syst) $\pm$ 0.7 (modeling) fb, in agreement with the
next-to-leading order quantum chromodynamics prediction. The analysis is
extended with a search for the associated production of the Higgs boson and a
photon, which is generated by a coupling of the Higgs boson to light quarks.
The result is used to constrain the Higgs boson couplings to light quarks.
