Re: vertical spacing scrambles systems

[Keith OHara]

Eluze <eluzew <at> gmail.com> writes:

> when I (re-)read the passage about modifying alists in NR (chapter 5.3.6)
> I'm getting a bit confused: there is an example how to set all values to
> zero and it lists every available parameter and sets it to zero:
> 
> \new PianoStaff \with {
> \override StaffGrouper.staff-staff-spacing =
>   #'((basic-distance . 0)
>   (minimum-distance . 0)
>   (padding . 0)
>   (stretchability . 0))
> }
> 
> but it would be much easier (and sufficient) to write
> 
> \override StaffGrouper.staff-staff-spacing = #'((basic-distance . 0))
>

Well, easier to type, but hard to understand because it removes the 
definitions of an unknown number (currently 3) of other parameters.
 
> tbh - I was only half-aware of the fact that alists are always completely
> overridden when one is not using nested overrides - partly probably because
> the doc speaks of /default-when-unset/ values (where are these values set?)

/default-when-unset/ is a strange concept.  When 'stretchability is unset, 
LilyPond tries to look up its value, finds none, and then tries to behave 
reasonably. In the context of staff-staff-spacing, the programmer decided 
that stretching proportional to 'basic-distance was reasonable.  I don't see 
any reason to describe these failsafe behaviors in the documentation, 
because users can explicitly request the 'stretchability they want.

> or /files being loaded each time an input file is compiled/ 

This probably refers to 'paper-defaults-init.ly' and 'engraver-init.ly'
and 'define-grobs.scm'  where things like the default spacing between
PianoStaves and such things are defined.