eractive elements. DIP would block that same-origin access.
	 *
	 * Keyed off $pagenow rather than the current screen so the guard keeps
	 * working if the header set-up is ever moved to an earlier hook (such as
	 * admin_init) where the screen is not yet available.
	 */
	global $pagenow;

	// phpcs:ignore WordPress.Security.NonceVerification.Recommended
	if ( 'site-editor.php' === $pagenow && ! wp_is_block_theme() && ( ! isset( $_GET['p'] ) || '/' === $_GET['p'] ) ) {
		return;
	}

	/*
	 * Skip when a third-party page builder overrides the block editor.
	 * DIP isolates the document into its own agent cluster,
	 * which blocks same-origin iframe access that these editors rely on.
	 */
	if ( isset( $_GET['action'] ) && 'edit' !== $_GET['action'] ) {
		return;
	}

	// Cross-origin isolation is not needed if users can't upload files anyway.
	if ( ! current_user_can( 'upload_files' ) ) {
		return;
	}

	wp_start_cross_origin_isolation_output_buffer();
}

/**
 * Sends the Document-Isolation-Policy header for cross-origin isolation.
 *
 * Uses an output buffer to add crossorigin="anonymous" where needed.
 *
 * @since 7.1.0
 */
function wp_start_cross_origin_isolation_output_buffer(): void {
	$chromium_version = wp_get_chromium_major_version();

	if ( null === $chromium_version || $chromium_version < 137 ) {
		return;
	}

	ob_start(
		static function ( string $output ): string {
			header( 'Document-Isolation-Policy: isolate-and-credentialless' );

			return wp_add_crossorigin_attributes( $output );
		}
	);
}

/**
 * Adds crossorigin="anonymous" to relevant tags in the given HTML string.
 *
 * @since 7.1.0
 *
 * @param string $html HTML input.
 * @return string Modified HTML.
 */
function wp_add_crossorigin_attributes( string $html ): string {
	$site_url = site_url();

	$processor = new WP_HTML_Tag_Processor( $html );

	// See https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/crossorigin.
	$cross_origin_tag_attributes = array(
		'AUDIO'  => array( 'src' ),
		'LINK'   => array( 'href' ),
		'SCRIPT' => array( 'src' ),
		'VIDEO'  => array( 'src', 'poster' ),
		'SOURCE' => array( 'src' ),
	);

	while ( $processor->next_tag() ) {
		$tag = $processor->get_tag();

		if ( ! isset( $cross_origin_tag_attributes[ $tag ] ) ) {
			continue;
		}
		$crossorigin = $processor->get_attribute( 'crossorigin' );
		if ( null !== $crossorigin ) {
			continue;
		}

		if ( 'AUDIO' === $tag || 'VIDEO' === $tag ) {
			$processor->set_bookmark( 'audio-video-parent' );
		}

		$processor->set_bookmark( 'resume' );

		$sought = false;

		$is_cross_origin = false;

		foreach ( $cross_origin_tag_attributes[ $tag ] as $attr ) {
			$url = $processor->get_attribute( $attr );
			if ( is_string( $url ) && ! str_starts_with( $url, $site_url ) && ! str_starts_with( $url, '/' ) ) {
				$is_cross_origin = true;
			}

			if ( $is_cross_origin ) {
				break;
			}
		}

		if ( $is_cross_origin ) {
			if ( 'SOURCE' === $tag ) {
				$sought = $processor->seek( 'audio-video-parent' );

				if ( $sought ) {
					$processor->set_attribute( 'crossorigin', 'anonymous' );
				}
			} else {
				$processor->set_attribute( 'crossorigin', 'anonymous' );
			}

			if ( $sought ) {
				$processor->seek( 'resume' );
				$processor->release_bookmark( 'audio-video-parent' );
			}
		}
	}

	return $processor->get_updated_html();
}

0/24 (TEST-NET-1).
				|| ( 192 === $parts[0] && 88 === $parts[1] && 99 === $parts[2] )   // 192.88.99.0/24 (6to4 relay anycast).
				|| ( 198 === $parts[0] && 51 === $parts[1] && 100 === $parts[2] )  // 198.51.100.0/24 (TEST-NET-2).
				|| ( 203 === $parts[0] && 0 === $parts[1] && 113 === $parts[2] )   // 203.0.113.0/24 (TEST-NET-3).
				|| ( 169 === $parts[0] && 254 === $parts[1] )                      // 169.254.0.0/16 (link-local and cloud metadata).
				|| ( 100 === $parts[0] && 64 <= $parts[1] && 127 >= $parts[1] )    // 100.64.0.0/10 (CGNAT).
				|| ( 198 === $parts[0] && 18 <= $parts[1] && 19 >= $parts[1] )     // 198.18.0.0/15 (benchmarking).
				|| ( 224 <= $parts[0] && 239 >= $parts[0] )                        // 224.0.0.0/4 (multicast).
				|| 240 <= $parts[0]                                                // 240.0.0.0/4 (reserved, includes 255.255.255.255 broadcast).
			) {
				// If host appears local, reject unless specifically allowed.
				/**
				 * Checks if HTTP request is external or not.
				 *
				 * Allows to change and allow external requests for the HTTP request.
				 *
				 * @since 3.6.0
				 *
				 * @param bool   $external Whether HTTP request is external or not.
				 * @param string $host     Host name of the requested URL.
				 * @param string $url      Requested URL.
				 */
				if ( ! apply_filters( 'http_request_host_is_external', false, $host, $url ) ) {
					return false;
				}
			}
		}
	}

	if ( empty( $parsed_url['port'] ) ) {
		return $url;
	}

	$port = $parsed_url['port'];

	/**
	 * Controls the list of ports considered safe in HTTP API.
	 *
	 * Allows to change and allow external requests for the HTTP request.
	 *
	 * @since 5.9.0
	 *
	 * @param int[]  $allowed_ports Array of integers for valid ports. Default allowed ports
	 *                              are 80, 443, and 8080.
	 * @param string $host          Host name of the requested URL.
	 * @param string $url           Requested URL.
	 */
	$allowed_ports = apply_filters( 'http_allowed_safe_ports', array( 80, 443, 8080 ), $host, $url );
	if ( is_array( $allowed_ports ) && in_array( $port, $allowed_ports, true ) ) {
		return $url;
	}

	if ( $parsed_home && $same_host && isset( $parsed_home['port'] ) && $parsed_home['port'] === $port ) {
		return $url;
	}

	return false;
}

/**
 * Marks allowed redirect hosts safe for HTTP requests as well.
 *
 * Attached to the {@see 'http_request_host_is_external'} filter.
 *
 * @since 3.6.0
 *
 * @param bool   $is_external
 * @param string $host
 * @return bool
 */
function allowed_http_request_hosts( $is_external, $host ) {
	if ( ! $is_external && wp_validate_redirect( 'http://' . $host ) ) {
		$is_external = true;
	}
	return $is_external;
}

/**
 * Adds any domain in a multisite installation for safe HTTP requests to the
 * allowed list.
 *
 * Attached to the {@see 'http_request_host_is_external'} filter.
 *
 * @since 3.6.0
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param bool   $is_external
 * @param string $host
 * @return bool
 */
function ms_allowed_http_request_hosts( $is_external, $host ) {
	global $wpdb;
	static $queried = array();
	if ( $is_external ) {
		return $is_external;
	}
	if ( get_network()->domain === $host ) {
		return true;
	}
	if ( isset( $queried[ $host ] ) ) {
		return $queried[ $host ];
	}
	$queried[ $host ] = (bool) $wpdb->get_var( $wpdb->prepare( "SELECT domain FROM $wpdb->blogs WHERE domain = %s LIMIT 1", $host ) );
	return $queried[ $host ];
}

/**
 * A wrapper for PHP's parse_url() function that handles consistency in the return values
 * across PHP versions.
 *
 * Across various PHP versions, schemeless URLs containing a ":" in the query
 * are being handled inconsistently. This function works around those differences.
 *
 * @since 4.4.0
 * @since 4.7.0 The `$component` parameter was added for parity with PHP's `parse_url()`.
 *
 * @link https://www.php.net/manual/en/function.parse-url.php
 *
 * @param string $url       The URL to parse.
 * @param int    $component The specific component to retrieve. Use one of the PHP
 *                          predefined constants to specify which one.
 *                          Defaults to -1 (= return all parts as an array).
 * @return mixed False on parse failure; Array of URL components on success;
 *               When a specific component has been requested: null if the component
 *               doesn't exist in the given URL; a string or - in the case of
 *               PHP_URL_PORT - integer when it does. See parse_url()'s return values.
 *
 * @phpstan-param int<-1, 7> $component
 * @phpstan-return (
 *     $component is -1
 *         ? false|array{
 *               scheme?: string,
 *               host?: string,
 *               port?: int<0, 65535>,
 *               user?: string,
 *               pass?: string,
 *               path?: string,
 *               query?: string,
 *               fragment?: string,
 *           }
 *         : (
 *             $component is 2
 *                 ? int<0, 65535>|null
 *                 : string|null
 *         )
 * )
 */
function wp_parse_url( $url, $component = -1 ) {
	$to_unset = array();
	$url      = (string) $url;

	if ( str_starts_with( $url, '//' ) ) {
		$to_unset[] = 'scheme';
		$url        = 'placeholder:' . $url;
	} elseif ( str_starts_with( $url, '/' ) ) {
		$to_unset[] = 'scheme';
		$to_unset[] = 'host';
		$url        = 'placeholder://placeholder' . $url;
	}

	$parts = parse_url( $url );

	if ( false === $parts ) {
		// Parsing failure.
		return $parts;
	}

	// Remove the placeholder values.
	foreach ( $to_unset as $key ) {
		unset( $parts[ $key ] );
	}

	return _get_component_from_parsed_url_array( $parts, $component );
}

/**
 * Retrieves a specific component from a parsed URL array.
 *
 * @internal
 *
 * @since 4.7.0
 * @access private
 *
 * @link https://www.php.net/manual/en/function.parse-url.php
 *
 * @param array|false $url_parts The parsed URL. Can be false if the URL failed to parse.
 * @param int         $component The specific component to retrieve. Use one of the PHP
 *                               predefined constants to specify which one.
 *                               Defaults to -1 (= return all parts as an array).
 * @return mixed False on parse failure; Array of URL components on success;
 *               When a specific component has been requested: null if the component
 *               doesn't exist in the given URL; a string or - in the case of
 *               PHP_URL_PORT - integer when it does. See parse_url()'s return values.
 *
 * @phpstan-param false|array{
 *     scheme?: string,
 *     host?: string,
 *     port?: int<0, 65535>,
 *     user?: string,
 *     pass?: string,
 *     path?: string,
 *     query?: string,
 *     fragment?: string,
 * } $url_parts
 * @phpstan-param int<-1, 7> $component
 * @phpstan-return (
 *     $component is -1
 *         ? false|array{
 *               scheme?: string,
 *               host?: string,
 *               port?: int<0, 65535>,
 *               user?: string,
 *               pass?: string,
 *               path?: string,
 *               query?: string,
 *               fragment?: string,
 *           }
 *         : (
 *             $component is 2
 *                 ? int<0, 65535>|null
 *                 : string|null
 *         )
 * )
 */
function _get_component_from_parsed_url_array( $url_parts, $component = -1 ) {
	if ( -1 === $component ) {
		return $url_parts;
	}

	$key = _wp_translate_php_url_constant_to_key( $component );
	if ( false !== $key && is_array( $url_parts ) && isset( $url_parts[ $key ] ) ) {
		return $url_parts[ $key ];
	} else {
		return null;
	}
}

/**
 * Translates a PHP_URL_* constant to the named array keys PHP uses.
 *
 * @internal
 *
 * @since 4.7.0
 * @access private
 *
 * @link https://www.php.net/manual/en/url.constants.php
 *
 * @param int $constant PHP_URL_* constant.
 * @return string|false The named key or false.
 *
 * @phpstan-param int<-1, 7> $constant
 * @phpstan-return 'scheme'|'host'|'port'|'user'|'pass'|'path'|'query'|'fragment'|false
 */
function _wp_translate_php_url_constant_to_key( $constant ) {
	$translation = array(
		PHP_URL_SCHEME   => 'scheme',
		PHP_URL_HOST     => 'host',
		PHP_URL_PORT     => 'port',
		PHP_URL_USER     => 'user',
		PHP_URL_PASS     => 'pass',
		PHP_URL_PATH     => 'path',
		PHP_URL_QUERY    => 'query',
		PHP_URL_FRAGMENT => 'fragment',
	);

	return $translation[ $constant ] ?? false;
}