Thanks David for the explanation!


> Le 20 avr. 2017 à 08:51, David Kastrup <> a écrit :
> Jacques Menu Muzhic <> writes:
>> Hello David,
>>> LilyPond 3 could be a rework of the optimization engine doing away with
>>> the hard pure/unpure distinction.
>> Not sure I understand this, can you tell us more?
> It's not a user-level distinction.  LilyPond currently makes line breaks
> first, page breaks afterwards.  Page break decisions do not influence
> the line break decisions.  Grobs/callbacks basically have to declare
> whether they are dependent on line break decisions or not and use
> different mechanisms and callbacks if they are.  That's awkward because
> there often are very rare circumstances where this makes a difference in
> results.
> It's the main source of unexpected interactions when refining
> typesetting stuff and consequently a major roadblock for
> extending/fixing LilyPond: quite often a change has consequences where
> other stuff is falling apart unexpectedly.  That makes a lot of the
> typesetting a mine field mostly navigatable by "backend experts" since
> they have experience patching up the things falling apart as they go.
> -- 
> David Kastrup

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