code: def enter_node(self, ir_node):
          
          this_is_cdata = (isinstance(ir_node, Element)
                           and ir_node.name in self.cdata_elements)
          self.state['is_cdata'] = bool(self.state.get('is_cdata')) or this_is_cdata
docs: Enter the given element; keeps track of `cdata`;
          subclasses may extend by overriding