I don’t know if this is accepted in MusicXML definition or if it’s an error, but Dorico exports beam ‘forward hook’ and ‘backward hook’ using ‘start’ instead of backward/forward in the beams tags.
Thanks for reporting this, alvira. You’re quite right that Dorico doesn’t seem to handle partial beams correctly when exporting MusicXML at the moment. I’ve made a note of this and we will fix this in due course.
Both Dorico and Sibelius import the XML files correctly. So, I fixed my code. You’re the best in support, Daniel!