code: def mimetype(self):
          
          if ';' in self.headers.get('Content-Type', ''):
              return self.headers['Content-Type'].split(';')[0]
          return self.headers.get('Content-Type', self.static_format)
docs: Get the Content-Type header from the response. Strip
          the ";charset=xxxxx" portion if necessary. If we can't
          find it, use the predefined format.