Checks for CRTF compatibility.

def check_crtf(self):
        """
        Checks for CRTF compatibility.
        """
        if self.region_type not in regions_attributes:
            raise ValueError("'{0}' is not a valid region type in this package"
                             "supported by CRTF".format(self.region_type))

        if self.coordsys not in valid_coordsys['CRTF']:
            raise ValueError("'{0}' is not a valid coordinate reference frame in "
                             "astropy supported by CRTF".format(self.coordsys))