  In a unifying way, the doorway mechanism explains spectral properties in a
rich variety of open mesoscopic quantum systems, ranging from atoms to nuclei.
A distinct state and a background of other states couple to each other which
sensitively affects the strength function. The recently measured superscars in
the barrier billiard provide an ideal model for an in--depth investigation of
this mechanism. We introduce two new statistical observables, the full
distribution of the maximum coupling coefficient to the doorway and directed
spatial correlators. Using Random Matrix Theory and random plane waves, we
obtain a consistent understanding of the experimental data.
