Re: Determining what parameters exist for an item

[Simon Albrecht]

On 24.01.2016 18:22, Kieren MacMillan wrote:
> Lilypond has grobs, and those grobs have properties, and those properties have 
> values,

I think the point is that some properties either do not have values at 
all, or those values are determined during compilation, depending on 
other circumstances.

>   and the default values of some of those properties are not easily 
> determinable by the [beginning?] user.
>
> Three examples which I just pulled at total random are
>      Beam.beam-thickness (via beam-interface)

Beam thickness is certainly a multiple of staff line thickness, so its 
value can’t be told in general.

>      NoteHead.break-visibility (via item-interface)

This is clearly a property which is unset, and remains unset, and for 
good reasons: Why would the visibility of a NoteHead depend on line 
breaks? In fact, tests show that a NoteHead is always considered to be 
‘unbroken’ (= mid-line), so \override NoteHead.break-visibility = ##(#t 
#f #t) will make all NoteHeads invisible, and the first and third values 
in the vector don’t matter at all.

>      KeyCancellation.font-size (via font-interface)

It turns out that this can’t be overridden at all.

I hope this helps enlighten matters.

Best, Simon