the perturbative regime of non-overlapping (isolated) resonances to the so-called Ericsson regime of strong overlap. These mechanisms and their related spectral effects have been experimentally studied in various context: in microwave cavities [@Men03; @Bar05; @Dietz06; @Hem06; @Kuhl08], in optical microcavities [@Fang07; @Leb07; @Rex02], and in elastodynamics [@Lobkis00; @Lobkis03].

The most salient feature of open systems is the set of resonances which are quasibound states embedded in the continuum. A natural way to address them analytically is via the energy-dependent scattering matrix, $S(E)$. Following the Heidelberg approach [@Verb85], the poles (i.e., resonances) of the $S$ matrix turn out to be the complex eigenvalues of an effective non-Hermitian Hamiltonian ${\mathcal{H}_{\mathrm{eff}}}$, whereas the bi-orthogonal eigenvectors of the latter determine the corresponding resonance states (quasimodes). Universal properties of resonance scattering in the chaotic regime can then be analyzed by applying random matrix theory (RMT) that amounts to replacing the actual non-Hermitian Hamiltonian with an RMT ensemble of the appropriate symmetry class [@Guh98]. The main advantage of such an approach is that it treats on equal footing both the spectral and scattering characteristics of open chaotic systems as well as that it is flexible enough to incorporate other imperfections of the system, e.g., disorder and 