get_the_category_rss( string $type = null ): string

381function get_the_category_rss( $type = null ) {382	if ( empty( $type ) ) {383		$type = get_default_feed();384	}385	$categories = get_the_category();386	$tags       = get_the_tags();387	$the_list   = '';388	$cat_names  = array();389 390	$filter = 'rss';391	if ( 'atom' === $type ) {392		$filter = 'raw';393	}394 395	if ( ! empty( $categories ) ) {396		foreach ( (array) $categories as $category ) {397			$cat_names[] = sanitize_term_field( 'name', $category->name, $category->term_id, 'category', $filter );398		}399	}400 401	if ( ! empty( $tags ) ) {402		foreach ( (array) $tags as $tag ) {403			$cat_names[] = sanitize_term_field( 'name', $tag->name, $tag->term_id, 'post_tag', $filter );404		}405	}406 407	$cat_names = array_unique( $cat_names );408 409	foreach ( $cat_names as $cat_name ) {410		if ( 'rdf' === $type ) {411			$the_list .= "\t\t<dc:subject><![CDATA[$cat_name]]></dc:subject>\n";412		} elseif ( 'atom' === $type ) {413			$the_list .= sprintf( '<category scheme="%1$s" term="%2$s" />', esc_attr( get_bloginfo_rss( 'url' ) ), esc_attr( $cat_name ) );414		} else {415			$the_list .= "\t\t<category><![CDATA[" . html_entity_decode( $cat_name, ENT_COMPAT, get_option( 'blog_charset' ) ) . "]]></category>\n";416		}417	}418 419	/**420	 * Filters all of the post categories for display in a feed.421	 *422	 * @since 1.2.0423	 *424	 * @param string $the_list All of the RSS post categories.425	 * @param string $type     Type of feed. Possible values include 'rss2', 'atom'.426	 *                         Default 'rss2'.427	 */428	return apply_filters( 'the_category_rss', $the_list, $type );429}