code: def osd_page_handler(config=None, identifier=None, prefix=None, **args):
      
      template_dir = os.path.join(os.path.dirname(__file__), 'templates')
      with open(os.path.join(template_dir, 'testserver_osd.html'), 'r') as f:
          template = f.read()
      d = dict(prefix=prefix,
               identifier=identifier,
               api_version=config.api_version,
               osd_version='2.0.0',
               osd_uri='/openseadragon200/openseadragon.min.js',
               osd_images_prefix='/openseadragon200/images',
               osd_height=500,
               osd_width=500,
               info_json_uri='info.json')
      return make_response(Template(template).safe_substitute(d))
docs: Flask handler to produce HTML response for OpenSeadragon view of identifier.
  
      Arguments:
          config - Config object for this IIIF handler
          identifier - identifier of image/generator
          prefix - path prefix
          **args - other aguments ignored