When a connector is drawn to link two shapes together, it gets attached to a certain point on both shapes. These points are typically those that show red squares when you are attaching them to a connector. Sometimes you may attach your connector to the wrong red square, and may need to detach it from that point, and attach it somewhere else. Or maybe you connected to the wrong shape altogether, and now want to detach the connector from one shape and attach it to another.
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