By elementary hadron we mean a compact bound state of quarks as opposite to a composite hadron, which is made up by other elementary hadrons. To decide the structure of exotic hadrons one may either look for patterns in spectroscopy, as the quark model suggests, or resort to the physics of shallow bound states, virtual states, cusps etc. In recent times, following an experimental study by the LHCb collaboration, a discussion has been raised on the role of the scattering effective range r0 as a discriminating parameter between the elementary and composite hypotheses for the X(3872). I will present a brief introduction to this topic.