(MEI.shared) Groups elements that may appear as part of the music element.
<music>Contains a single musical text of any kind, whether unitary or composite, for example,
an etude, opera, song cycle, symphony, or anthology of piano solos.
<music>Contains a single musical text of any kind, whether unitary or composite, for example,
an etude, opera, song cycle, symphony, or anthology of piano solos.