
| X | Music |
| Xa | Music : theory |
| Xb | Music : history |
| Xd | Music for keyboard instruments |
| Xe | Music for stringed instruments |
| Xf | Music for wind instruments |
| Xg | Music for plectral instruments |
| Xh | Music for drums and percussion instruments |
| Xi | Electronic instruments |
| Xk | Instrumental ensembles |
| Xl | Orchestras |
| Xm | Instrumental music : other |
| Xo | Solo voice |
| Xp | Choirs |
| Xq | Vocal music : other |
| Xqh | Songs |
| Xqhz | Popular songs and chants |
| Xqj | Children's songs |
| Xr | Dramatic vocal music |
| Xs | Sacred music. Liturgy and ritual |
| Xu | Western traditional music |
| Xv | Non-western traditional music |
| Xx | Jazz, rock, and other popular music |
| Xy | Lyrics to vocal and dramatic music. Librettos |