In the example on the documentation page
http://lilypond.org/doc/v2.19/Documentation/learning/building-a-score-from-scratch
the command
\override VerticalAxisGroup.staff-staff-spacing.stretchability = 5
is used to modify the spacing of the pedal staff in an organ score.
The result shown on the documentation page (which I also get at home
with 2.19.80) does not match the result on the corresponding page for
2.18, and is clearly wrong.
I cannot find any documentation suggesting that the usage should have
changed.
Regards,
Paul