+Environments such as;
+
+@example
+\begin@{lilypond@} @dots{} \end@{lilypond@}
+@end example
+
+@noindent
+are not interpreted by @LaTeX{}. Instead, @code{lilypond-book} extracts
+those @q{environments} into files of its own and runs LilyPond on them.
+It then takes the resulting graphics and creates a @file{.tex} file
+where the @code{\begin@{lilypond@}}@dots{}@code{\end@{lilypond@}} macros
+are then replaced by @q{graphics inclusion} commands. It is at this
+time that @LaTeX{} is run (although @LaTeX{} will have run previously,
+it will have been, effectively, on an @q{empty} document in order to
+calculate things like @code{\linewidth}).
+