Merge pull request #236 from r-gaia-cs/core-subheading

    # Dict of tuples for each callout type: {style: (title, min, max)}

    CALLOUTS = {}

    WARN_ON_EXTRA_HEADINGS = True  # Warn when other headings are present?

    WARN_ON_EXTRA_HEADINGS = False  # Warn when other headings are present?

    # Validate YAML doc headers: dict of {header text: validation_func}

    DOC_HEADERS = {}

        The top-level document has no headings indicating subtopics.

        The only valid subheadings are nested in blockquote elements"""

        heading_nodes = self.ast.get_section_headings()

        if len(heading_nodes) == 0:

            return True

        if len(heading_nodes) != 0:

            # Individual heading msgs are logged by validate_section_heading_order

        logging.error(

            logging.warning(

                "In {0}: "

            "The topic page should not have sub-headings "

            "outside of special blocks. "

            "If a topic needs sub-headings, "

            "it should be broken into multiple topics.".format(self.filename))

        return False

                "Sub-headings are often a sign "

                "a lesson needs to be split into multiple topics. "

                "Please make sure this subsection doesn't belong "

                "in a separate lesson.".format(self.filename))

        return True

    def _run_tests(self):

        parent_tests = super(TopicPageValidator, self)._run_tests()