Re: Contexts affected by \override and \overrideProperty

[Urs Liska]

Am 19.02.19 um 12:27 schrieb David Kastrup:
> Urs Liska <address@hidden> writes:
>
> > Am 18.02.19 um 17:30 schrieb David Kastrup:
> > > Urs Liska <address@hidden> writes:
> > >
> > > > Can someone explain to me why \overrideProperty Staff.BarLine.color
> > > > #red colors the barlines in *all* staves while \override
> > > > Staff.BarLine.color = #red only affects the current Staff context?
> > > >
> > > > I have just re-read
> > > > http://lilypond.org/doc/v2.19/Documentation/notation/set-versus-override
> > > > and am scratching my head. I do claim to have some experience by now
> > > > but this page isn't actually really helpful:
> > > >
> > > >      "The commands ... |\overrideProperty| change grob properties by
> > > >      bypassing all context properties completely and, instead, catch
> > > >      grobs as they are being created, setting properties on them ... for
> > > >      a specific override."
> > > >
> > > > This doesn't give a clue when \overrideProperty should (or must) be
> > > > used instead of \override or what the difference in behaviour actually
> > > > is.
> > > >
> > > > \overrideProperty is also present on
> > > > http://lilypond.org/doc/v2.19/Documentation/notation/available-music-functions#index-overrideProperty-1
> > > >
> > > >      |overrideProperty| [music] - grob-property-path (list of indexes or
> > > >      symbols) value (any type)
> > > >          Set the grob property specified by grob-property-path to value.
> > > >          grob-property-path is a symbol list of the form
> > > >          |Context.GrobName.property| or |GrobName.property|, possibly
> > > >          with subproperties given as well.
> > > >
> > > >          As opposed to |\override| which overrides the context-dependent
> > > >          defaults with which a grob is created, this command uses
> > > >          |Output_property_engraver| at the grob acknowledge stage. This
> > > >          may be necessary for overriding values set after the initial
> > > >          grob creation.
> > > >
> > > > This gives an indication for why it may in some cases be necessary to
> > > > use \overrideProperty but it doesn't explain why it seems to affect
> > > > objects in all contexts instead of just the one where it is used.
> > > Because the respective engraver is only active at Score level and
> > > overrides the properties in _all_ contexts of the given type.
> >
> > So this means that if I'm in the situation where I'm forced to use
> > \overrideProperty this property will always be overridden on the Score
> > context?
> No, just in all Staff contexts (if Staff is what you specified).  The
> Score context property will remain unchanged.
>
> This does not sound overly useful, does it?


It *does* sound useful, just not for the problem at hand. I'm dealing 
with annotating music, and I would often have loved to have the 
possibility to "clone" one annotation through all related contexst (e.g. 
the given example of a barline. If I annotate that the source used a 
double barline that I corrected to a single one I will often want to 
have it visible on all staves.)
This is currently the behaviour for the non-rhythmic music events but 
not for others.

Knowing this it seems I have to find a way to avoide using 
\overrideProperty somewhere in my engraver, which seems somewhat 
daunting at this point. OTOH it may open up a way to *selectively* use 
this behaviour for *all* music types.

Urs


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