code: def to_html(graph: BELGraph, chart: Optional[str] = None) -> str:
      
      with open(os.path.join(HERE, 'index.html'), 'rt') as f:
          html_template = Template(f.read())
  
      return html_template.render(**_get_context(graph, chart=chart))
docs: Render the graph as an HTML string.
  
      Common usage may involve writing to a file like:
  
      >>> from pybel.examples import sialic_acid_graph
      >>> with open('ideogram_output.html', 'w') as file:
      ...     print(to_html(sialic_acid_graph), file=file)