public static function is_valid_rule( $rule ) {
		if ( empty( $rule ) ) {
			return false;
		}

		if ( empty( $rule['url_path'] ) ) {
			return false;
		}

		// We allow no filter at all.
		if ( '' === $rule['key'] ) {
			return true;
		}

		/**
		 * If the operator is greater than or less than and there is no
		 * comparison value or a comparison value that is not a number, you
		 * might have a bad time.
		 */
		if ( ( empty( $rule['value'] ) || ! is_numeric( $rule['value'] ) )
			&& ( 'less_than' === $rule['operator'] || 'greater_than' === $rule['operator'] )
		) {
			return false;
		}

		/**
		 * If the key points to a value that is not a number and the operator
		 * is less than or greater than, you might have a bad time.
		 */
		if ( ! INVP::meta_value_is_number( apply_filters( 'invp_prefix_meta_key', $rule['key'] ) )
			&& ( 'less_than' === $rule['operator'] || 'greater_than' === $rule['operator'] )
		) {
			return false;
		}

		return true;
	}