docs: def remove_child(self, child):
          """
          Remove a child from this node.
          """
          assert child in self.children
          self.children.remove(child)
          self.index.pop(child.tax_id)
          if child.parent is self:
              child.parent = None
          if child.index is self.index:
              child.index = None
  
          # Remove child subtree from index
          for n in child:
              if n is child:
                  continue
              self.index.pop(n.tax_id)
              if n.index is self.index:
                  n.index = None