Re: Issue 1427 in lilypond: \bookpart stored in a variable can't contain markup

[lilypond]

Comment #1 on issue 1427 by PhilEHolmes: \bookpart stored in a variable  
can't contain markup
http://code.google.com/p/lilypond/issues/detail?id=1427

Neil Puttock commented:

The same happens for page-markers (i.e., \break, \pageBreak, \label, etc.):

mypart = \bookpart {
  \label #'foo
}

% also crashes
\bookpart { \mypart }

It seems that when a book is cloned, the copy constructor assumes all
elements in the original book to be scores, which is unsafe: the
elements can also be markup or page-markers:

#(display (ly:score? (car (ly:book-scores mypart))))

-> #f