The tone poems of Richard Strauss are noted as the high point of program music in the latter part of the 19th century, extending its boundaries and taking the concept of realism in music to an unprecedented level. In these works, he widened the expressive range of music while depicting subjects many times thought unsuitable for musical depiction. As Hugh MacDonald points out in the New Grove Dictionary of Music and Musicians, "In the years prior to World War I these works were held to be in the vanguard of modernism."