Subclasses may override this method.

def _clear(self, contours=True, components=True, anchors=True,
               guidelines=True, image=True):
        """
        Subclasses may override this method.
        """
        if contours:
            self.clearContours()
        if components:
            self.clearComponents()
        if anchors:
            self.clearAnchors()
        if guidelines:
            self.clearGuidelines()
        if image:
            self.clearImage()