code: def _header(self):
          
          html = """
  		<!DOCTYPE html>
  		<html lang="en">
  		<head>
  			<meta charset="utf-8">
  			<title>Report</title>
  		"""
          if "bokeh" in self.report_engines:
              html += self.bokeh_header_()
          if "altair" in self.report_engines:
              html += self.altair_header_()
          if "chartjs" in self.report_engines:
              html += self.chartjs_header_()
          html += """
  		</head>
  		<body>
  		"""
          return html
docs: Default html header