intercepting implicit/explicit page breaks

[Knut Petersen]

Hi everybody!

I use

#(define (display-breaks grob)
   (if (and (grob::has-interface grob 'paper-column-interface)
            (eq? #t (ly:grob-property grob 'non-musical)))
       (if (eq? 1 (ly:item-break-dir grob))
           (let* ((moment (ly:grob-property grob 'when))(m moment)
                  (bar (ly:grob-property grob 'rhythmic-location))(b (car bar)))
                 (format out "~a new system at bar ~a~%" (format-moment m) b)
             ))
       (ly:message "Need NonMusicalPaperColumn grob to determine line 
breaks.")))

activated by

     \override NonMusicalPaperColumn #'after-line-breaking = #display-breaks

That reliably gives the moment and bar number of an implicit or explicit break,
but I also need to know if this break is a PAGE break.

I assume the information is not available at the time of the callback used 
above, but
that isn't a problem as it would be used by a script after lilypond has 
finished.

Any idea where/when to get that information from lilypond?

thx,
 Knut