static function cleanUp( $string ) {
		if ( NORMALIZE_INTL ) {
			$string = self::replaceForNativeNormalize( $string );
			$norm = normalizer_normalize( $string, Normalizer::FORM_C );
			if ( $norm === null || $norm === false ) {
				# normalizer_normalize will either return false or null
				# (depending on which doc you read) if invalid utf8 string.
				# quickIsNFCVerify cleans up invalid sequences.

				if ( self::quickIsNFCVerify( $string ) ) {
					# if that's true, the string is actually already normal.
					return $string;
				} else {
					# Now we are valid but non-normal
					return normalizer_normalize( $string, Normalizer::FORM_C );
				}
			} else {
				return $norm;
			}
		} elseif ( self::quickIsNFCVerify( $string ) ) {
			# Side effect -- $string has had UTF-8 errors cleaned up.
			return $string;
		} else {
			return self::NFC( $string );
		}
	}