How to change 'line-count along the way

[Anders Vinjar]

Im a lilypond-newbie, used to be working with CMN, now i've
searched around abit in docs and on the net without finding any
solutions.  Ive got 2 questions hopefully someone might be able
to answer.

Is there a way to specify "running" values for the property
#'line-count of 'StaffSymbol?  Ie. changing the number of
staff-lines in the middle of a line, at a bar or some such?  To
achieve input along the following:


When notating with non-standard number of staff-lines, how to
avoid getting extra leger-lines on notes?  Related to this, how
to avoid the vertical scaling of the content (note-placements and
stem-lengths etc.)

The following score sets up a staff with 3 lines taking the
vertical space of a 5-line staff.  

\version "2.2.0"
\score{
    \notes\relative c'{
        d e g a e' f g a
    }
    \paper{
        \context { \StaffContext
                   \override StaffSymbol #'line-count = #3
                   \override StaffSymbol #'extra-offset = #'(0.0 . -1.0)
                   \override StaffSymbol #'staff-space = #(/ 5 3)
               }
    }
}

I guess what's needed is a pointer to the actual drawing-function
for StaffSymbol's (the Staffs 'engraver is it?), or examples of
variants.

Anders Vinjar