[ramblurr]

It also affects the digital markup of music. Music can't be expressed with a tree structure as there is lots of overlap.

A simple example is a slur. It crosses bar lines. <bar1> ... <slur> ... </bar1> ... </slur> <bar2> uhoh!

In fact there are many mutually incompatible hierarchies in music engraving.

It's funny though MusicXML is a popular interchange format, but internally looks nothing like what one would naively expect.

[afandian]

Ditto control flow. It’s tempting to think of repeat bars, DC al fines, codas etc hierarchical structures when in fact they are imperative GOTOs and always have been.