'Add or remove the clicked area from the selection
Args:
area (QRect): the area that is clicked
event (QEvent): event description'

def select_area(self, area, event):

    if (event.button() != Qt.LeftButton):
        return
    index = self.areas.index(area)
    if (event.modifiers() & Qt.ControlModifier):
        self.selection ^= {index}
    else:
        self.selection = {index}
    self.update_selection()
