11.2.3—That protons and neutrons are not fundamental particles and describe protons

A proton has composition uud and a neutron udd; neither is fundamental because each contains three valence quarks bound by the strong interaction.

Use quark composition to derive charge and distinguish valence content from the fluctuating sea of quantum field theory.

Replacing one up quark in uud with a down quark gives udd, changing a proton into a neutron and reducing charge by e.

“Three quarks” is the simple valence model, not a claim that no gluons or transient pairs are present.