code: def as_txt(self):
          
          s = "IIIF Image Server Error\n\n"
          s += self.text if (self.text) else 'UNKNOWN_ERROR'
          s += "\n\n"
          if (self.parameter):
              s += "parameter=%s\n" % self.parameter
          if (self.code):
              s += "code=%d\n\n" % self.code
          for header in sorted(self.headers):
              s += "header %s=%s\n" % (header, self.headers[header])
          return s
docs: Text rendering of error response.
  
          Designed for use with Image API version 1.1 and above where the
          error response is suggested to be text or html but not otherwise
          specified. Intended to provide useful information for debugging.