X00 Subfield $r - Key for music: [600, 700, 800]

Subfield $r contains the statement of key in which the music is written; used in a uniform title for a work in a name/title field.

Example:

700 12$aBeethoven, Ludwig van,$d1770-1827.$tSonatas,$mpiano,$nno. 13, op. 27, no. 1,$rE major.$f1986.