Panerusan
The panerusan instruments or elaborating instruments are one of the divisions of instruments used in Indonesian gamelan. Instead of the rhythmic structure provided by the colotomic instruments, and the core melody of the balungan instruments, the panerusan instruments play variations on the balungan. They are usually the most difficult instruments to learn in the gamelan, but provide the most opportunity for improvisation and creativity in the performer. Panerusan instruments include the gendér, suling, rebab, siter/celempung, bonang, and gambang. The female singer, the pesindhen, is also often included, as she sings in a similar fashion to the instrumental techniques . As these include the only wind instruments, string instruments, and wooden percussion instruments found in the gamelan, they provide a timbre which stands out from most of the gamelan. The notes that the panerusan instruments play are largely in melodic formulas known as cengkok and sekaran. These are selected from a huge collection which every performer carries in his head, based on the patet, mood, and traditions surrounding a piece. Sekaran. Sekaran (Javanese for "flowering") is a type of elaboration used in the Javanese gamelan, especially on the "bonang barung". It is similar to the "cengkok" of other elaborating instruments  in its floridity and openness to improvisation, but a "sekaran" generally happens only at the end of a "nongan" or other colotomic division. It is usually preceded by "imbal", an interlocking pattern between the "bonang barung" and the "bonang panerus". Different "sekaran" are used in different "pathet", but there are always a variety available. A good "bonang" player will choose a "sekaran" based on how the other instruments and the "sindhen" are improvising. Traditionally the "bonang panerus" did not play "sekaran", and simply continued in the "imbal" pattern, but now some players use "sekaran", as long as they maintain the  fast character of typical "bonang panerus" parts.