The MusicXML DTD’s 3.0 specify that:
The number attribute is used to distinguish overlapping
and nested part-groups, not the sequence of groups.
and nested part-groups, not the sequence of groups.
In 2014, see https://forums.makemusic.com/viewtopic.php?f=12&t=2730, Michael Good mentions that he hasn’t got any example exhibiting overlapping part groups:
by Hans Vereyken » Mon Oct 20, 2014 2:20 am:Hi Michael,Thanks for the quick reply.I can't think of any score where one would need overlapping groups, if I look at it, it always is possible (and more clear) with nested groups. Can you give me an example of a score that needs overlapping groups to get correct results? I did search for this situations in experimental scores but even there I couldn't find an example.by Michael Good » Tue Oct 21, 2014 8:59 am:Hi Hans,I don't have an example right now. I would expect it wouldn't be too hard to find in (for instance) manuscripts where barlines across staves and brackets may have been drawn inconsistently.
And in https://forums.makemusic.com/viewtopic.php?f=12&t=2149&p=5425&hilit=overlapping+default+x+part+groups#p5425, we learn that default-x is the way to decipher such groups:
Michael Good wrote:Bonjour Hervé,There is no hierarchy implied in part-group elements. All that matters is the sequence of part-group elements relative to score-part elements. The sequencing of two consecutive part-group elements does not matter. It is the default-x attribute that indicates the left-to-right ordering of the group symbols.
So my question is: has anyone ever seen a use case for overlapping, non-nested part groups?
LilyPond's unofficial example 41f-StaffGroups-Overlapping.xml displays as the attached image in Finale 2014 after moving the bracket for ‘Group 2’ slightly to the left:
but musicxml2ly handles ‘Group 2' differently:
Thanks if can bring light to this topic!
JM