More research on Srebotnjak:
Yugoslavia / Die neue Musik in Jugoslawien by Dragotin Cvetko from  The World of Music, Vol. 4, No. 3 (JUNE 1962), pp. 52-53: Srebotnjak used "pointillist technique"? "Serial pointillist technique"?

Music in Slovenia by Niall O'Loughlin from The Musical Times, Vol. 134, No. 1801 (Mar., 1993), pp. 130-133: He had come to London to study with Peter Racine Fricker in 1959-60. Preludes was written in 60. He also used "12 note technique". (Except in Harp Concerto where he used 8-note to facilitate pedaling.)


Contemporary Trends in Yugoslav Music by Zija Kučukalić from International Review of the Aesthetics and Sociology of Music, Vol. 2, No. 2 (Dec., 1971), pp. 271-273: "the Slovenian folk music tradition is attached to the folk music of the Alps region and that is one of musical communication and closeness with other nations."

Music in Slovenia. In the First of Two Articles, Niall O'Loughlin Introduces the Rich Musical Heritage of One of Europe's Most Newly Independent Countries by Niall O'Loughlin from The Musical Times, Vol. 134, No. 1800 (Feb., 1993), pp. 74-77[Journal]: "Hindemith served as the model for many other younger composers in the 1950s,"

Music in Yugoslavia by Everett Helm from The Musical Quarterly, Vol. 51, No. 1, Special Fiftieth Anniversary Issue: Contemporary Music in Europe: A Comprehensive Survey (Jan., 1965), pp. 215-224: Srebotnjak's early works were Expressionist.

Oxford Music Online
Among composers of his generation, Srebotnjak had the most distinctively expressionist style, despite the diversity of his techniques, which ranged from 12-note composition (Invenzione variata) and serialism (Serenata, Monologi, Šest skladb, Antifona) to aleatory works and graphic scores. He often integrated folklore elements (Slovene and Macedonian) into his works and used expanded variations of the themes of other composers (Kogoj, Osterc, Tartini, Škerjanc).