aligning RehearsalMarks outside staff area

[Graham Percival]

A few months ago, I could put RehearsalMarks outside the staff boundary 
box, but the changes to Y-offset-callbacks result in this code not 
working.

Parsing...marks.ly:1:20: While evaluating arguments to list in 
expression (list Self_alignment_interface::aligned_on_parent):
marks.ly:1:20: Unbound variable: 
Self_alignment_interface::aligned_on_parent

Does anybody know how to do this with the new callback code?
- Graham


\version "2.7.15"
{
\override RehearsalMark #'Y-offset-callbacks = #(list
      Self_alignment_interface::aligned_on_parent )
\clef bass
c''4 c'' c'' c''
\mark \default
c'' c'' c'' c''
}