Song, poem, or verse.
The following, in order:
<label> Label (of an Equation, Figure, Reference, etc.), zero or one
<title> Title, zero or one
<subtitle> Document Subtitle, zero or one
One or more of any of:
<verse-line> Line of a Verse
<verse-group> Verse Form for Poetry
Any combination of:
<attrib> Attribution
<permissions> Permissions