What a navigation (a plain, non-extending arrow move) does to the current selection — orthogonal
to ShapePolicy, which governs the resulting shape:
'clear'(default) — drop the whole selection back to the single anchor cell (the spreadsheet
cursor: an arrow moves the cursor and forgets any multi-selection).
'modify' — re-scope the active range in place, preserving the other ranges (a range
picker moving one reference of many; the sibling references stay put).
What a navigation (a plain, non-extending arrow move) does to the current selection — orthogonal to ShapePolicy, which governs the resulting shape:
'clear'(default) — drop the whole selection back to the single anchor cell (the spreadsheet cursor: an arrow moves the cursor and forgets any multi-selection).'modify'— re-scope the active range in place, preserving the other ranges (a range picker moving one reference of many; the sibling references stay put).