-at the top of the main input file). With @code{relative-includes}
-set, the path for each @code{\include} command will be taken
-relative to the file containing that command. This behavior is
-recommended and it will become the default behavior in a future
-version of lilypond.
+at the top of the main input file).
+
+When @code{relative-includes} is set to @code{#t}, the path for each
+@code{\include} command will be taken relative to the file containing
+that command. This behavior is recommended and it will become the
+default behavior in a future version of lilypond.
+
+Files relative to the main directory and files relative to some other
+directory may both be @code{\include}d by setting
+@code{relative-includes} to @code{#t} or @code{#f} at appropriate
+places in the files. For example, if a general library, libA, has
+been created which itself uses sub-files which are @code{\include}d
+by the entry file of that library, those @code{\include} statements
+will need to be preceded by
+@code{#(ly:set-option #relative-includes #t)} so they are interpreted
+correctly when brought into the main @code{.ly} file, like this:
+
+@example
+libA/
+ libA.ly
+ A1.ly
+ A2.ly
+ ...
+@end example
+
+@noindent
+then the entry file, @code{libA.ly}, will contain
+
+@example
+#(ly:set-option 'relative-includes #t)
+\include "A1.ly"
+\include "A2.ly"
+...
+% return to default setting
+#(ly:set-option 'relative-includes #f)
+@end example
+
+Any @file{.ly} file can then include the entire library simply with
+
+@example
+\include "~/libA/libA.ly"
+@end example
+
+More complex file structures may be devised by switching at
+appropriate places.