\offset and mutable properties

[Simon Albrecht]

Hello,

while developing a workaround (or solution?) for issue 4316 
<https://code.google.com/p/lilypond/issues/detail?id=4316>, I 
encountered the following problem: \offset cannot be used on X and Y 
offset properties, apparently because these are mutable, and as the doc 
string for (offsetter) in scm/music-functions.scm states, \offset is 
limited to work only on immutable properties. (I haven’t really gotten 
behind the distinction of mutable/immutable properties…)
Now, I don’t really know how to circumvent this, and it seems like a 
really important usecase for \offset. Do you have any ideas here?

For more context, see issue 4316 and the current version of the \off 
function I’m developing (attached; I hope it’s readable by the comments 
I gave).

TIA,
Simon

offII.ly
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