docs: def set_content(self, content):
          """Set textual content for the object/node.
  
          Verifies the node is allowed to contain content, and throws an
          exception if not.
          """
          if self.allows_content:
              self.content = content.strip()
          else:
              raise UNTLStructureException(
                  'Element "%s" does not allow textual content' % (self.tag,)
              )