Selection.focusNode read-only property returns the
Node in which the selection ends.
A user may make a selection from left to right (in document order) or right to left (reverse of document order). The focus is where the user ended the selection. This can be visualized by holding the Shift key and pressing the arrow keys on your keyboard to modify the current selection. The selection's focus moves, but the selection's anchor, the other end of the selection, does not move.
node = sel.focusNode
The definition of 'Selection.focusNode' in that specification.
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Selection, the interface it belongs to.