I think that the purpose of down arrow and up arrow is make a transposition but i think that Shift + down arrow, Shift + up arrow should be select up and down measures.
Add "Alt" to your Shift+Up/Down to make it extend the selection. True, it's not as standard a shortcut for this purpose as Shift+Up/Down, but in a notation program, it's also going to be a less common operation than changing pitch.
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That is the purpose of this operation.
I think that the purpose of down arrow and up arrow is make a transposition but i think that Shift + down arrow, Shift + up arrow should be select up and down measures.
Thanks
"up/down" is "semitone up(prefer sharp)/down(prefer flat)"
"Shift+up/down" is "Diatonic step up/down"
"Ctrl+up/down" is "Octave up/down"
Check the shortcuts in Edit → Preferences
Add "Alt" to your Shift+Up/Down to make it extend the selection. True, it's not as standard a shortcut for this purpose as Shift+Up/Down, but in a notation program, it's also going to be a less common operation than changing pitch.