+@cindex transparent objects
+@cindex removing objects
+@cindex hiding objects
+@cindex invisible objects
+The following example demonstrates how to connect different voices
+using ties. Normally, ties only connect two notes in the same
+voice. By introducing a tie in a different voice,
+
+@lilypond[fragment,relative=2]
+ << {
+ b8~ b8\noBeam
+ } \\ {
+ b[ g8]
+ } >>
+@end lilypond
+
+@noindent
+and blanking the first up-stem in that voice, the tie appears to cross
+voices:
+
+@lilypond[fragment,relative=2,verbatim]
+ << {
+ \once \override Stem #'transparent = ##t
+ b8~ b8\noBeam
+ } \\ {
+ b[ g8]
+ } >>
+@end lilypond
+
+@item
+The @code{padding} property for objects with
+@cindex @code{padding}
+@code{side-position-interface} can be set to increase distance between
+symbols that are printed above or below notes. We only give an
+example; a more elaborate explanation is in @ref{Constructing a
+tweak}:
+
+@lilypond[fragment,relative=1,verbatim]
+ c2\fermata
+ \override Script #'padding = #3
+ b2\fermata
+@end lilypond
+
+@end itemize
+
+More specific overrides are also possible. The next section
+discusses in depth how to figure out these statements for yourself.
+
+
+@node Constructing a tweak
+@subsection Constructing a tweak
+
+The general procedure of changing output, that is, entering
+a command like
+
+@example
+ \override Voice.Stem #'thickness = #3.0
+@end example
+
+@noindent
+means that we have to determine these bits of information:
+
+@itemize
+@item the context: here @context{Voice}.
+@item the layout object: here @code{Stem}.
+@item the layout property: here @code{thickness}
+@item a sensible value: here @code{3.0}
+@end itemize
+
+
+@cindex internal documentation
+@cindex finding graphical objects
+@cindex graphical object descriptions
+@cindex tweaking
+@cindex @code{\override}
+@cindex @code{\set}
+@cindex internal documentation
+
+We demonstrate how to glean this information from the notation manual
+and the program reference.
+
+@node Navigating the program reference
+@subsection Navigating the program reference
+
+Suppose we want to move the fingering indication in the fragment
+below:
+
+@lilypond[fragment,relative=2,verbatim]
+c-2
+\stemUp
+f
+@end lilypond
+
+If you visit the documentation on fingering instructions (in
+@ref{Fingering instructions}), you will notice that there is written:
+
+@quotation
+@seealso
+
+Program reference: @internalsref{FingerEvent} and @internalsref{Fingering}.
+
+@end quotation
+
+
+
+This fragment points to two parts of the program reference: a page
+on @code{FingerEvent} and on @code{Fingering}.
+
+The page on @code{FingerEvent} describes the properties of the music
+expression for the input @code{-2}. The page contains many links
+forward. For example, it says
+
+@quotation
+ Accepted by: @internalsref{Fingering_engraver},
+@end quotation
+
+@noindent
+That link brings us to the documentation for the Engraver, the
+plug-in, which says
+
+@quotation
+ This engraver creates the following layout objects: @internalsref{Fingering}.
+@end quotation
+
+In other words, once the @code{FingerEvent}s are interpreted, the
+@code{Fingering_engraver} plug-in will process them.
+The @code{Fingering_engraver} is also listed to create
+@internalsref{Fingering} objects,
+
+
+ Lo and behold, that is also the
+second bit of information listed under @b{See also} in the Notation
+manual. By clicking around in the program reference, we can follow the
+flow of information within the program, either forward (like we did
+here), or backwards, following links like this:
+
+@itemize @bullet
+
+@item @internalsref{Fingering}:
+ @internalsref{Fingering} objects are created by:
+ @b{@internalsref{Fingering_engraver}}
+
+@item @internalsref{Fingering_engraver}:
+Music types accepted: @b{@internalsref{fingering-event}}
+@item @internalsref{fingering-event}:
+Music event type @code{fingering-event} is in Music expressions named
+@b{@internalsref{FingerEvent}}
+@end itemize
+
+This path goes against the flow of information in the program: it
+starts from the output, and ends at the input event.
+
+The program reference can also be browsed like a normal document. It
+contains a chapter on
+@ifhtml
+@internalsref{Music-definitions},
+@end ifhtml
+@ifnothtml
+@code{Music definitions}
+@end ifnothtml
+on @internalsref{Translation}, and the @internalsref{Backend}. Every
+chapter lists all the definitions used, and all properties that may be
+tuned.
+
+
+@node Layout interfaces
+@subsection Layout interfaces
+
+@cindex interface, layout
+@cindex layout interface
+
+The HTML page which we found in the previous section, describes the
+layout object called @internalsref{Fingering}. Such an object is a
+symbol within the score. It has properties, which store numbers (like
+thicknesses and directions), but also pointers to related objects. A
+layout object is also called @emph{grob},