code: def setup(self, parent=None, previous=None):
          
          self.parent = parent
          self.previous = previous
          self.next = None
          self.previousSibling = None
          self.nextSibling = None
          if self.parent and self.parent.contents:
              self.previousSibling = self.parent.contents[-1]
              self.previousSibling.nextSibling = self
docs: Sets up the initial relations between this element and
          other elements.