Re: Set vs. Override - I'm confused

[Michael Brennan]

Erik Sandberg wrote:
> > Great!  You now officially know more about this area than me, because I 
> > don't have a clue when to use \override or \set.  Please take a few 
> > minutes to send me some clarifications or additions for the manual:
> > http://lilypond.org/web/devel/participating/documentation-adding
> >     
My simple understanding of it is that:
\set sets a property for the whole context, and the objects contained in 
that context while
\override is for a particular graphical object.

Just a little explanation like that, that separates them would be good 
to have in the docs,
or better yet, Eric's more thorough explanation below.

> Hm. Here's my understanding of it:
>
> You can say it's all about the granularity of the setting. \override
> manipulates
> settings which are specific to one graphical object/grob (e.g. a NoteHead).
> \set
> changes settings on a higher level, and can modify more than one type of grob.
> For example, fontSize is a context property (modified with \set) because it
> changes the behaviour of several different types of grobs (e.g., noteheads and
> rests). You can also change the fontsize of all noteheads only, by overriding a
> grob property of NoteHead grobs only. Or you can modify the fontsize of a
> single
> notehead using \tweak.
>   
> You can notice that \set and \override use different syntaxes:
> \set ctx.prop = val
> \override ctx Grob.prop = val
> Rule of thumb is: If you can figure out a type of Grob that the tweak is
> specific to, then it's probably an \override.
>
> This rule requires a rough knowledge of which grob types that exist. The only
> way I know to get this knowledge is by reading the internals reference.
>
> Erik
>
>   

What is a \tweak? I can't recall reading about it in the manual. You say 
that you can modify
the fontsize of a single notehead with \tweak. Would that give any 
difference than using a
\once \override NoteHead #'font-size = size