code: def validate(self):
          
          from .files import HTMLZipFile
          try:
              assert self.kind == content_kinds.HTML5, "Assumption Failed: Node should be an HTML5 app"
              assert self.questions == [], "Assumption Failed: HTML should not have questions"
              assert any(filter(lambda f: isinstance(f, HTMLZipFile), self.files)), "Assumption Failed: HTML should have at least one html file"
              return super(HTML5AppNode, self).validate()
  
          except AssertionError as ae:
              raise InvalidNodeException("Invalid node ({}): {} - {}".format(ae.args[0], self.title, self.__dict__))
docs: validate: Makes sure HTML5 app is valid
              Args: None
              Returns: boolean indicating if HTML5 app is valid