Jerum!
In the second scene of this opera, one character confesses not to know what the "Marker" does, after which another character explains the rules to him while drawing a parallel to the cobbling trade. To prevent one character from serenading another in this opera, a third sings "Jerum! Jerum!" A side plot concerns the romance between David and Magdalene, and at a meeting of the title group, one of them named Veit Pogner sings "Das schone Fest, Johannistag," outlining the contest that will take place on that festival day. Walther triumphs over Sixtus Beckmesser for the hand of Eva in, for ten points, what this Richard Wagner whose title characters include Fritz Kothner, Augustin Moser, and Hans Sachs, all singers in the titular city.
In the second scene of this opera, one character confesses not to know what the "Marker" does, after which another character explains the rules to him while drawing a parallel to the cobbling trade.
Die {Meistersinger von Nurnberg} or The {Mastersingers of Nuremberg}