+After page breaks are determined, the vertical spacing within each
+system is reevaluated in order to fill the page more evenly; if a page
+has space left over, systems are stretched in order to fill that space.
+The amount of stretching can be configured though the @code{max-stretch}
+property of the @internalsref{VerticalAlignment} grob. By default,
+@code{max-stretch} is set to zero, disabling stretching. To enable
+stretching, a sane value for @code{max-stretch}
+is @code{ly:align-interface::calc-max-stretch}.
+
+In some situations, you may want to stretch most of a system while
+leaving some parts fixed. For example, if a piano part occurs in the
+middle of an orchestral score, you may want to leave the piano staves
+close to each other while stretching the rest of the score. The
+@code{keep-fixed-while-stretching} property of
+@internalsref{VerticalAxisGroup} can be used to achieve this. When set
+to @code{##t}, this property keeps its staff (or line of lyrics) from
+moving relative to the one directly above it. In the example above,
+you would override @code{keep-fixed-while-stretching} to @code{##t} in
+the second piano staff:
+
+@lilypond[verbatim]
+#(set-default-paper-size "a6")
+#(set-global-staff-size 14.0)
+
+\book {
+\paper {
+ ragged-last-bottom = ##f
+}
+
+\new Score \with
+{
+ \override VerticalAlignment #'max-stretch = #ly:align-interface::calc-max-stretch
+}
+{
+\new GrandStaff
+<<
+ \new StaffGroup
+ <<
+ \new Staff {c' d' e' f'}
+ \new Staff {c' d' e' f'}
+ \new Staff {c' d' e' f'}
+ >>
+
+ \new PianoStaff
+ <<
+ \new Staff {c' d' e' f'}
+ \new Staff \with {
+ \override VerticalAxisGroup #'keep-fixed-while-stretching = ##t
+ }
+ {c' d' e' f'}
+ >>
+
+ \new StaffGroup
+ <<
+ \new Staff {c' d' e' f'}
+ \new Staff {c' d' e' f'}
+ >>
+>>
+}
+}
+@end lilypond