Question: What concept did the father of Siegfried Wagner revolutionize?

Context articles: List of operas by Siegfried Wagner
Verena Wagner Lafferentz
Friedelind Wagner
Winifred Wagner
Siegfried Wagner
Carmen Reppel
Der Bärenhäuter (opera)
Richard Wagner
An allem ist Hütchen schuld!
Wolfgang Wagner

This is a complete list of the operas of the German composer Siegfried Wagner (1869–1930), the son of Richard Wagner (1813–1883).
Verena Wagner Lafferentz (born 2 December 1920) is the fourth child and youngest daughter of Winifred and Siegfried Wagner and the granddaughter of German composer Richard Wagner.
Friedelind Wagner (29 March 1918 – 8 May 1991) was the daughter of German opera composer Siegfried Wagner and his English wife, Winifred Williams and the granddaughter of the composer Richard Wagner.
 Born in Bayreuth, she was known by the nickname "Die Maus" or "Mausi".
 Along with other members of her family, from early in life Friedelind Wagner was involved with the Bayreuth Festspielhaus.
 In 1936, she began work as an assistant to Heinz Tietjen but her outspoken criticism of close family friend Adolf Hitler and the policies of the Third Reich led to her leaving Germany in 1939.
 She lived for a short time in Switzerland before emigrating first to England where she began writing anti-Nazi columns for the "Daily Sketch" newspaper.
Winifred Wagner (born Winifred Marjorie Williams; 23 June 1897 – 5 March 1980) was the English-born wife of Siegfried Wagner, the son of Richard Wagner, and ran the Bayreuth Festival after her husband's death in 1930 until the end of World War II in 1945.
 She was a friend and supporter of Adolf Hitler (himself a Wagner enthusiast), and she and Hitler maintained a regular correspondence.
Siegfried Wagner (6 June 18694 August 1930) was a German composer and conductor, the son of Richard Wagner.
 He was an opera composer and the artistic director of the Bayreuth Festival from 1908 to 1930.
Carmen Reppel is a German soprano active in both opera and concert.
 A member of the Staatstheater Hannover , she had a major international career, appearing in leading roles in over 60 operas.
 She also explored lesser-known repertoire such as Siegfried Wagner's "Schwarzschwanenreich " and appeared in contemporary operas, singing in world premieres of operas by Aribert Reimann and Flavio Testi.
 She is known for her parts in the "Jahrhundertring ", the centenary production of Wagner's "Der Ring des Nibelungen" at the Bayreuth Festival, including the filmed version of 1980.
Der Bärenhäuter is an 1899 German-language opera by Siegfried Wagner based on the German folk tale Der Bärenhäuter, or the Bearskin man.
 As with most of Siegfried Wagner's operas it is more influenced by his teacher Humperdinck than his father Richard Wagner's operas.
Wilhelm Richard Wagner ( ; ] ; 22 May 181313 February 1883) was a German composer, theatre director, polemicist, and conductor who is primarily known for his operas (or, as some of his later works were later known, "music dramas").
 Unlike most opera composers, Wagner wrote both the libretto and the music for each of his stage works.
 Initially establishing his reputation as a composer of works in the romantic vein of Weber and Meyerbeer, Wagner revolutionised opera through his concept of the "Gesamtkunstwerk" ("total work of art"), by which he sought to synthesise the poetic, visual, musical and dramatic arts, with music subsidiary to drama.
 He described this vision in a series of essays published between 1849 and 1852.
 Wagner realised these ideas most fully in the first half of the four-opera cycle "Der Ring des Nibelungen" ("The Ring of the Nibelung").
An allem ist Hütchen schuld!
 ('Hattie is to blame for everything!')
, Op.
 11, is an opera in German in three acts composed by Siegfried Wagner in 1914/15 to his own libretto.
 It is described as a "Märchenspiel" or fairy-tale play.
 It premiered on 6 December 1917 at the court theatre ("Hoftheater ") in Stuttgart.
Wolfgang Wagner (30 August 191921 March 2010) was a German opera director.
 He is best known as the director (Festspielleiter) of the Bayreuth Festival, a position he initially assumed alongside his brother Wieland in 1951 until the latter's death in 1966.
 From then on, he assumed total control until he retired in 2008, although many of the productions which he commissioned were severely criticized in their day.
 He had been plagued by family conflicts and criticism for many years.
 He was the son of Siegfried Wagner, the grandson of Richard Wagner, and the great-grandson of Franz Liszt.