If this option is turned on, then the Rectangular Mode fence will be used for the visualization of screen area where the 'Click Test' will be performed. This provides a method for verifying and identifying those areas on the sceen which are valid for the selection of objects. For the each pixel of the specified area (by Rectangular Mode fence) the virtual 'mouse click' will be performed. If the user clicks on a pixel that will allow a graphic to be selected, then those pixels are colored by the graphic's color. If there are selected graphics, then other graphics are ignored. The test takes into account the 'Aperture size', Render Mode and Layer's styles.
Example of Click Test: