I was attempting to help someone understand all the markings in a piece with which they are unfamiliar. One, however, has given me pause:
Now, I know the rule for a trill is that it ordinarily remains diatonic. If a chromatic trill is needed, an accidental will be placed near the tr marking (or occasionally with grace notes).
What I am not sure about is whether an accidental earlier in the measure also affects the auxiliary or upper note of the trill.
In this specific case, should one trill D-E or D-E♭?
(I would like an authoritative answer, as I plan to also use this to tell the people at MuseScore how the trill should work. Currently, they do an E♭ for the first quarter note, but then switch to an E♮ across the bar. I know that's wrong, but I want to have a definitive answer before reporting a bug.)