MusicXML - the duration element
Observed on MuseScore 3.5.2/Windows 7
The MusicXML documentation is a bit opaque regarding the intended significance of the duration element (used within a note element).
Some workers in the field believe that the duration element is just an alternate, numeric way to specify the time value of a note (whether it is a quarter note, half note, etc.), always matching the type element, which gives the time value as a name ("quarter"). Some passages in the documentation in fact seem to "suggest" this.
But if we persist in our study, we eventually realize that the intent is for the element *duration" to define the intended "play duration" of the note.
Upon the import of a MusicXML file, MuseScore seemingly interprets a duration element for a note as telling how long after the beginning of the note the next note should begin to sound. And the play durations of all the notes created are the durations implied by their time values.
We see this in this screen shot of the Piano Roll editor for the score created from a small MusicXML file. All notes are quarter notes.
For the first note in the second measure (the G), the value of duration in the MusicXML file was 75% of the time value of the note. We see that in the reconstructed score, its play duration is "100% of face value", just as for all the notes. But the start time of the second note has been moved forward to start just "75% of a quarter note" after the start of the measure (and the rest of the notes in the measure slide forward with it).
Incidentally, this curious situation causes MuseScore to report, when we attempt to load this MusicXML file, that the format is invalid.
In fact, I believe that, barring the use of certain specialized MusicXML attributes (attack, release), the duration element should control the play duration of the note, and the play of all notes should start at the normal point implied by the musical time for the note.
In MuseScore, we have the ability to adjust the play duration of any note. When we export a MusicXML file from a score in which notes have had their play durations adjusted from the "default" values , the duration element for every note nevertheless corresponds exactly to the time value of the note, rather than reflecting the play duration set by the scorist.