LMB-drag always selects a span. LMB-click just defines a start, a span without length. It could be like placing a cursor in text-editing.
The span itself should be visualized. Overlapping notes are selected. There could be a command to reduce the selection to notes that are entirely within the span.
If a span is empty and in a single row, it should be turned into a note automaticaly.
Ctrl-LMB: add span
Shift-LMB: edit existing spans
Alt/Meta-LMB: move span
F: fill in note(s). If the span is more than 1 row high, a chord menu could appear [Return key comes to mind, but is in use for “Playhead to Edit”]
The following actions either work by holding down the key, stopping by releasing it, or pressing the key short and terminating with a click:
- M: move
- A: move note_on
- Z: move note_off
- V: adjust velocity