\documentclass[a4paper, 12pt]{article}

\usepackage{graphics}
\begin{document}


\subsection{LaTeX comments}
This is a line with lilypond code
after the comment char % \lilypond{\context Voice <<c' e' g'>>}
% \lilypond{\context Voice <<c' e' g'>>}

If you do not see any music above
this line, then lilypond-book is handling latex comments pretty well :-)

The following snippet is preceded by a comment that would start a lilypond
environment

%%\begin{lilypond}
{%
\parindent 0pt
\noindent
\ifx\preLilyPondExample \undefined
\else
  \expandafter\preLilyPondExample
\fi
\def\lilypondbook{}%
\input{1b/lily-d4314a79-systems.tex}
\ifx\postLilyPondExample \undefined
\else
  \expandafter\postLilyPondExample
\fi
}

A single-line comment inside a fragment does not confuse lilypond-book:

{%
\parindent 0pt
\noindent
\ifx\preLilyPondExample \undefined
\else
  \expandafter\preLilyPondExample
\fi
\def\lilypondbook{}%
\input{96/lily-c3e77d50-systems.tex}
\ifx\postLilyPondExample \undefined
\else
  \expandafter\postLilyPondExample
\fi
}

\end{document}