Not all applications that support both MusicXML import and export support exactly the same notations in both directions, but it is definitely fair to say that Dorico’s export is a lot more asymmetrical than most, and we are well aware of Dorico’s deficiencies in this department. I am also the person responsible for writing the marketing copy for Dorico, so you can blame me for that, too. I’m sorry that the copy is not sufficiently explicit about the things that are missing from MusicXML export.
Here is a non-exhaustive list of some of the things Dorico does not yet export:
– Any kind of versioning information (e.g. what version of Dorico was used to encode it)
– Accidentals
– Chord symbols
– Arbitrary text
– Barline types
– Rehearsal marks
– Microtonal accidentals
– Grace notes before barlines (other kinds of grace notes are OK)
– Some dynamics (things like rfz, fp – basic dynamics are OK)
– Instrument transposition
– Articulations
– Partial beams and beaming over rests (basic beaming is exported)
– Tempos
– Glissando lines
– Arpeggios
– Playing techniques
I hope that the above list will at least help to set your expectations for the current state of Dorico’s MusicXML export more realistically. Improving MusicXML export is a priority for us, but it has to compete with many other things for our limited development time.