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Shift-click nodes to add to the selection. Drag empty canvas to rubber-band select. Double-click empty canvas to add a node where you clicked. Middle-mouse drag or Pan toggle to pan the view. Wheel / Ctrl+wheel to zoom.
Click a node or connector to select. Shift-click to add another. Drag empty canvas to rubber-band select. Click a connector line to select it — a "+ label" pill appears so you can add or edit its label.