useSingleSelectedElement
useSingleSelectedElement():
SingleSelectedElement|null
Returns the currently-selected node + edge only when exactly one
element is selected, and null otherwise (zero selection or
multi-selection). Designed for the properties sidebar’s “edit one thing
at a time” UI; the equality check tolerates stable references on
node.data / edge.data so the hook doesn’t spam re-renders.
Returns
Section titled “Returns”SingleSelectedElement | null
The selected element wrapped in { node, edge } (each
independently nullable), or null when selection isn’t a single item.