Original: The relationship of the librettist ( that is , the writer of a libretto ) to the composer in the creation of a musical work has varied over the centuries , as have the sources and the writing techniques employed .
Simplified: In the 19th century Eugène Scribe wrote a very large number of libretti that were set to music by composers such as Meyerbeer , Auber , Bellini , Donizetti , Rossini and Verdi .