code: def depth(self) -> int:
          
          if len(self.children):
              return 1 + max([child.depth for child in self.children])
          else:
              return 1
docs: Depth of the citation scheme
  
          .. example:: If we have a Book, Poem, Line system, and the citation we are looking at is Poem, depth is 1
  
  
          :rtype: int
          :return: Depth of the citation scheme