Re: [Lilypond-auto] Issue 4083 in lilypond: \keepWithTag does not nest well

[lilypond]

Comment #11 on issue 4083 by address@hidden: \keepWithTag does not nest well
https://code.google.com/p/lilypond/issues/detail?id=4083

Regarding comment #6, Keith's \chooseWithTag implementation:
clearTag should likely rather use for-some-music rather than music-map:  
music-map does a lot of copying and other stuff.

music-choose uses "map" several times where it should be using "for-each"  
since the result is discarded anyway.

In programmatic use (used internally in some package for providing some  
feature), this seems like a reasonably nice option since one knows how the  
code is going to be organized.  However, to stop this with interfering with  
user-level use of \keepWithTag, either the user or the package still needs  
to declare his/her/its tags to be in a class of its own.

Maybe we should warn when \keepWithTag is being used with a tag not  
declared in a tag layer?  It would likely be a nuisance for existing code,  
but even existing code would get disrupted if it started using a package  
based on \chooseWithTag without explicitly declared tag group.  And if some  
package needs to declare a tag group anyway in order to cooperate reliably  
with unrelated main documents potentially using \keepWithTag, the  
motivation for using \chooseWithTag in the first place becomes  
questionable.  If we cannot factually avoid the price for \keepWithTag  
(namely declaring our tag groups), the additional fiddlishness of  
\chooseWithTag does not buy us anything.

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