code: def nodes(self, node=None):
          '''walks through tree and yields each node'''
          if node is None:
              for root in self.stack:
                  yield from self.nodes(root)
          else:
              yield node
              if node.is_container():
                  for child in node.children:
                      yield from self.nodes(childf nodes(self, node=None):
          '''walks through tree and yields each node'''
          if node is None:
              for root in self.stack:
                  yield from self.nodes(root)
          else:
              yield node
              if node.is_container():
                  for child in node.children:
                      yield from self.nodes(child)
docs: walks through tree and yields each node