Output the graph for HTML.  This will insert a PNG with clickable
    image map.

def html_visit_inheritance_diagram(self, node):
    # type: (nodes.NodeVisitor, inheritance_diagram) -> None
    """
    Output the graph for HTML.  This will insert a PNG with clickable
    image map.
    """
    graph = node['graph']

    graph_hash = get_graph_hash(node)
    name = 'inheritance%s' % graph_hash

    # Create a mapping from fully-qualified class names to URLs.
    graphviz_output_format = self.builder.env.config.graphviz_output_format.upper()
    current_filename = self.builder.current_docname + self.builder.out_suffix
    urls = {}
    for child in node:
        if child.get('refuri') is not None:
            if graphviz_output_format == 'SVG':
                urls[child['reftitle']] = os.path.join("..", child.get('refuri'))
            else:
                urls[child['reftitle']] = child.get('refuri')
        elif child.get('refid') is not None:
            if graphviz_output_format == 'SVG':
                urls[child['reftitle']] = os.path.join('..', current_filename + '#' + child.get('refid'))
            else:
                urls[child['reftitle']] = '#' + child.get('refid')

    dotcode = graph.generate_dot(name, urls, env=self.builder.env)
    render_dot_html(
        self, node, dotcode, {}, 'inheritance', 'inheritance',
        alt='Inheritance diagram of ' + node['content'],
        link_to_svg='<i class="fa fa-external-link" aria-hidden="true"></i>'' SVG')
    raise nodes.SkipNode