This tool has three modes, the second mode is used to split objects with a line. This mode is ideal for splitting objects like polygons, rectangles, etc. In this image you should notice that I'm trying to split a rectangle that is on top of two other rectangles. The new mode in Vectorworks 2014 allows you to split just the selected object. This is extremely useful. If you have previous versions of Vectorworks you can achieve the same thing using the Option all Alt key.
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