+/* basic_music is basically the same as composite_music but with
+ * context-prefixed music and lyricized music explicitly removed. The
+ * reason is that in a sequence
+ *
+ * \new Staff \new Voice { ... } \addlyrics { ... } \addlyrics { ... }
+ *
+ * we need to group both \addlyrics together (as they go with the same
+ * voice) but then combine them with \new Voice { ... }, meaning that
+ * combining \new Voice { ... } needs higher priority than
+ * { ... } \addlyrics, and *not* have \new Staff \new Voice { ... }
+ * combine before combining \new Voice { ... } \addlyrics: only one
+ * layer of context-prefixed music should assemble before \addlyrics
+ * is integrated. Total mess, and we sort this mess out with explicit
+ * rules preferring a single context-prefix.
+ */
+
+basic_music: