Reflection across a line
Translation of a quadrilateral across a line. Notice that the lines extending from one point to its corresponding point are bisected by the line of reflection. This means that to reflect a point, line, or object means to reconstruct it identical mirror image at exactly the same distance from the line/point of reflection. Try moving the line of reflection by grabbing point e to see what happens.
What happens if you change the shape of the object by grabbing and moving A, B, C, or D slightly? What happens if you move the the vertex across the line of reflection?