The music played is mainly tango, vals and milonga (as the musical genre). Most milongas are held on a regular basis (usually weekly), and they often begin with dancing classes and sometimes demonstration dances. Usually, three to four  songs of a kind are played in a row (this is called tanda) followed by a short musical break (called cortina) to clear the dancefloor and facilitate partner changes. There are a number of informal rules that dictate how dancers should choose their dancing partners.