Section “Troubleshooting” in Application Usage - LilyPond

Chapter 1: Running lilypond 13
Warning staff affinities should only decrease
This warning can appear if there are no staves in the printed output, for example if there are
just a ChordName context and a Lyrics context as in a lead sheet. The warning messages can
be avoided by making one of the contexts behave as a staff by inserting
\override VerticalAxisGroup.staff-affinity = ##f
at its start. For details, see “Spacing of non-staff lines” in Section “Flexible vertical spacing
within systems” in Notation Reference.
Error message unexpected \new
A \score block must contain a single music expression. If instead it contains several \new
Staff, \new StaffGroup or similar contexts introduced with \new without them being enclosed
in either curly brackets, { ... }, or double angle brackets, >, like this:
\score {
% Invalid! Generates error: syntax error, unexpected \new
\new Staff { ... }
\new Staff { ... }
}
the error message will be produced.
To avoid the error, enclose all the \new statements in curly or double angle brackets.
Using curly brackets will introduce the \new statements sequentially:
\score {
{
\new Staff { a' a' a' a' }
\new Staff { g' g' g' g' }
}
}
but more likely you should be using double angle brackets so the new staves are introduced in
parallel, i.e. simultaneously:
\score {
>
}