Semantics of \section

[Joel C. Salomon]

Obviously, all three options below produce identical output.  (And
also, I know that `\sectionLabel` does not need to be attached to a
`\section`.)

But is there a notion of which generally best represents the way music
is divided, clearer to the next reader of my code than the other
choices?

—Joel

\version "2.23.80"

% I. `\section` outside parts
SectA_I = {
  \sectionLabel "Section A"
  c' d' e' f'
}
SectB_I = {
  \sectionLabel "Section B"
  f' e' d' c'
}
I = {
  \SectA_I \section
  \SectB_I  \fine
}
\score { \I }

% II. `\section` at parts’ end
SectA_II = {
  \sectionLabel "Section A"
  c' d' e' f'
  \section
}
SectB_II = {
  \sectionLabel "Section B"
  f' e' d' c'
  \section
}
II = {
  \SectA_II
  \SectB_II
  \fine
}
\score { \II }

% III. `\section` at parts’ start
SectA_III = {
  \section
  \sectionLabel "Section A"
  c' d' e' f'
}
SectB_III = {
  \section
  \sectionLabel "Section B"
  f' e' d' c'
}
III = {
  \SectA_III
  \SectB_III
  \fine
}
\score { \III }