I´m interested in references to other works, styles and genres. Historically art music have often involved references to other periods and to other genres, i. e. folk music. Art music had also within itself a strong tradition to implicitly and explicitly refer to, e. g. when writing a symphony the composer in a way refers to all other symphonies ever written. In the high modernistic period (which I consider ended by the way) it was something of a taboo to use this kind references. At least was the end to make a clean start from tradition. But, although originality was a important virtue and the break with history was a important goal, modernism I believe was a tradition in itself. The fear of references ended with Schnittke and other pluralists using direct musical quotations in their works. Another 20th century movement has to be mentioned in this context - the neoclassical direction with its references to the classical, pre-classical and baroque periods; here references took an even more important role than in previous music, perhaps as some kind of reaction to the ahistoricism of modernism. Today contemporary music (and even more strongly contemporary art) is widely diverse in artistic styles and methods. It is as the modernistic project succeeded in its radical goals of originality and rootlessness, but ended up finishing off itself in the process; when the modernist direction finally suceeded in killing tradition there could exist no gathering movement and hence modernism had dematerialized itself. (This reflection I think is absolutely true regarding art, but regarding music modernism still takes its dying breaths.)  When tradition is dead and pluralism rules, references takes on a new role. You have the whole spectra from provocative appropriations and interventions to mere subtle implications of aspects of obsolete or popular cultures.