Re: Issue 1063 in lilypond: Reverting nested property fails to restore default value if preceded by override in same grob

[lilypond]

Comment #8 on issue 1063 by address@hidden: Reverting nested property fails  
to restore default value if preceded by override in same grob
http://code.google.com/p/lilypond/issues/detail?id=1063

Well, here is a first comment.  Properties are a complex thing tied into  
various layers of contexts and possibly overriden at different levels.   
Property alists for nested contexts are stored with a clever Scheme via  
conses of the actual alist to be used, and the tail of the alist belonging  
to a different context.  The various lists are not modified in-place but  
rather get stuff prepended and removed at front.  If the tail gets out of  
sync with the respective parent, update_grob_properties resynchronizes them.

In contrast, alists for nested properties are just copied around and  
modified accordingly.  For that reason, the difference between a copied  
subproperty (and sibling subproperties) from an outer context and a native  
subproperty is not preserved.

A revert of one subproperty can't determine whether its siblings originate  
as a (possibly outdated) copy of a parent context, or from setting it on  
its own.

I am having problems understanding how the nesting of properties inside of  
properties can be simpler to resolve than the nesting of properties inside  
of contexts.

I continue thinking about that.  External insights welcome.