High-order harmonic studies of the role of resonances on the temporal and efficiency characteristics of converted coherent pulses : different approaches -- Different theoretical approaches in plasma hhg studies at resonance conditions -- Comparison of resonance harmonics : experiment and theory -- Resonance enhancement of harmonics in metal-ablated plasmas : early studies -- Resonance processes in ablated semiconductors -- Resonance processes at different conditions of harmonic generation in laser-produced plasmas -- Comparison of the resonance-, nanoparticle-, and quasi-phase-matching-induced processes leading to the growth of high-order harmonic yield