WP_Theme_JSON::append_to_selector( string $selector, string $to_append ): string

1488	protected static function append_to_selector( $selector, $to_append ) {1489		if ( ! str_contains( $selector, ',' ) ) {1490			return trim( $selector, " \t\n" ) . $to_append;1491		}1492 1493		/**1494		 * Check for an opportunity to skip the more-costly selector splitting.1495		 * This should be possible if there are no comments, strings, functions,1496		 * URLs, escapes, or comment declaration openers (CDOs).1497		 *1498		 * Note that this means the fast-path will not apply for selectors like1499		 * the following incomplete list:1500		 *1501		 *  - `[class ~= "wide"]`1502		 *  - `.wp-block:is(.is-style-a, .is-style-b)`1503		 *  - `:nth-child(1)`1504		 *1505		 * These syntax forms all present opportunities where a comma may not1506		 * separate selectors. If none of the start characters are present,1507		 * there should be no way for a comma to mean anything other than a1508		 * comma token. The exception are syntax errors, which are not handled here.1509		 *1510		 * @see https://www.w3.org/TR/css-syntax-3/#parse-comma-separated-list-of-component-values1511		 */1512		if ( strlen( $selector ) === strcspn( $selector, '/\'"(<\\' ) ) {1513			return preg_replace( '~[ \t\n]*,[ \t\n]*~', "{$to_append}, ", trim( $selector, " \t\n" ) ) . $to_append;1514		}1515 1516		$new_selectors = array();1517		$selectors     = static::split_selector_list( $selector );1518		foreach ( $selectors as $sel ) {1519			$new_selectors[] = $sel . $to_append;1520		}1521		return implode( ', ', $new_selectors );1522	}