Producing a discontinuous selection is difficult
Consider the situation where I have a 4/4 treble-clef bar with eight quavers in voice 2, underlying a complicated melody in voice 1. I want to delete the quavers but leave the melody behind.
As per the manual, my primary options for selecting multiple elements are Shift+drag-LMB, or selecting the first element and then using Shift-and-arrow-keys to expand the selection to multiple elements.
In both cases, this currently produces a range selection, which does not discriminate between notes within a chord or voices within a stave - it simply selects a time-range across the entire stave. In this example, if I were to attempt to select only the quavers in voice 2, then the melody in voice 1 would also be selected.
I believe the prescribed way to deal with this is to either use selection filters or use the "Context menu/Select/All Similar Elements in Range Selection" option, but it would be much more convenient if we could handle this situation using only the mouse and keyboard on the canvas. Currently, my only option in this case would be to hold down the Ctrl key and individually click on all eight quavers!
When a discontinuous selection is active, it's currently possible to deselect individual elements using Ctrl+LMB. However, when a range selection is active, Ctrl+LMB on a selected item has no effect, and Ctrl+LMB on a non-selected item seems to be bugged - it dismisses the range selection without selecting the clicked item. I suggest that Ctrl+LMB should always select/deselect the clicked item. This will require Ctrl+LMB to sometimes convert a range selection into a discontinuous selection.
Drag selections (shift+LMB-drag) will currently select additional elements which lie outside of the drag rectangle, so that the resulting selection is always a range selection. I suggest that drag selections should not select any notes or rests other than those which are strictly within the drag rectangle. This will require drag selections to sometimes produce a discontinuous selection, rather than a range selection.