code: def rotation_to_apply(self, only90s=False, no_mirror=False):
          
          rotation = self.request.rotation_deg
          if (no_mirror and self.request.rotation_mirror):
              raise IIIFError(code=501, parameter="rotation",
                              text="This implementation does not support mirroring.")
          if (only90s and (rotation != 0.0 and rotation != 90.0 and
                           rotation != 180.0 and rotation != 270.0)):
              raise IIIFError(code=501, parameter="rotation",
                              text="This implementation supports only 0,90,180,270 degree rotations.")
          return(self.request.rotation_mirror, rotation)
docs: Check and interpret rotation.
  
          Returns a truth value as to whether to mirror, and a floating point
          number 0 <= angle < 360 (degrees).