Originally Posted by jpettit
Summary (so far) of proven repeatable (by many) import into BIAB issues:
- Wong Key <== root issue BIAB is importing in XML 3.0. All other apps are using 4.0.
- Wrong Time signature <== root issue BIAB is importing in XML 3.0. All other apps are using 4.0.
I don't believe this is the case - as far as I can tell there were no changes in the MusicXML 3.1 and 4.0 spec regarding key or time signature. These issues are separate, and we are working on them.

Originally Posted by jpettit
I recommend people read the Music XML 4.0 spec to understand its purpose:
https://www.w3.org/2021/06/musicxml40/
From reading that page, it seems like the MusicXML 4.0 spec is mostly about adding new features rather than removing old ones. There are a few deprecated elements from the 3.0 spec, but as far as I can tell we don't use those. Any MusicXML file that doesn't use the new features is still considered v4.0 compliant, provided it also doesn't use the deprecated elements.

Originally Posted by jpettit
I also brought it into Musecore and exported it as mxl 4.0 and strangely enough it was close to accurate when importing into BIAB. The only variation was an extra part break at the end of the song.
The extra part at the end is basically the difference between how BB and MusicXML structure a song, in that BB operates as "choruses" with the 2-bar ending happening outside of that, where MusicXML simply writes a bar at a time. When exporting a MusicXML file from BB, there is no way of flagging a particular bar as the "ending", so when that file is imported into BB it imports everything as the "chorus" - then, if you have automatic 2 bar endings enabled, BB adds that after the imported data.

Since we can't rewrite the MusicXML spec, the only workaround I can think of here is if we added a "song length" field when importing a MusicXML file, similar to the bar offset field. I'll add that as a feature request, but for now this problem is solved by manually changing the song length after importing an XML.

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