About sophisticated stuffing of elementary particle with a hadron charge inside
Well, at first they thought protons and neutrons that make up nuclei of atoms of matter are indivisible particles. That’s why they call them fundamental, but when in 1968 at SLAC fired nuclei by electrons fast enough, they found three point-like particles hanging within a volume that is occupied by a proton or neutron. At first, those nucleons’ constituents were called just partons, and the name quarks settled later. Namely quarks as well as leptons can be considered as being truly elementary, or fundamental, because they directly undergo fundamental interactions. Quarks are confined inside the volume of nucleon because of the strong interaction holding them back, which, however, doesn’t prevent quarks from ‘moving’ inside it. The proton and neutron are arranged almost identical, only one of the three quarks differs. It is discovered six types of quarks in total. In various combinations with each other and with antiquarks, they compose a lot of unstable particles including mesons and hyperons.