}
	}

	// For PHP versions that don't support HEIC images, extract the size info using Imagick when available.
	if ( wp_is_heic_image_mime_type( $image_mime_type ) ) {
		$editor = wp_get_image_editor( $filename );

		if ( is_wp_error( $editor ) ) {
			return false;
		}

		// If the editor for HEICs is Imagick, use it to get the image size.
		if ( $editor instanceof WP_Image_Editor_Imagick ) {
			$size = $editor->get_size();
			return array(
				$size['width'],
				$size['height'],
				IMAGETYPE_HEIF,
				sprintf(
					'width="%d" height="%d"',
					$size['width'],
					$size['height']
				),
				'mime' => 'image/heic',
			);
		}
	}

	// The image could not be parsed.
	return false;
}

/**
 * Extracts meta information about an AVIF file: width, height, bit depth, and number of channels.
 *
 * @since 6.5.0
 *
 * @param string $filename Path to an AVIF file.
 * @return array {
 *     An array of AVIF image information.
 *
 *     @type int|false $width        Image width on success, false on failure.
 *     @type int|false $height       Image height on success, false on failure.
 *     @type int|false $bit_depth    Image bit depth on success, false on failure.
 *     @type int|false $num_channels Image number of channels on success, false on failure.
 * }
 */
function wp_get_avif_info( $filename ) {
	$results = array(
		'width'        => false,
		'height'       => false,
		'bit_depth'    => false,
		'num_channels' => false,
	);

	if ( 'image/avif' !== wp_get_image_mime( $filename ) ) {
		return $results;
	}

	// Parse the file using libavifinfo's PHP implementation.
	require_once ABSPATH . WPINC . '/class-avif-info.php';

	$handle = fopen( $filename, 'rb' );
	if ( $handle ) {
		$parser  = new Avifinfo\Parser( $handle );
		$success = $parser->parse_ftyp() && $parser->parse_file();
		fclose( $handle );
		if ( $success ) {
			$results = $parser->features->primary_item_features;
		}
	}
	return $results;
}

/**
 * Extracts meta information about a WebP file: width, height, and type.
 *
 * @since 5.8.0
 *
 * @param string $filename Path to a WebP file.
 * @return array {
 *     An array of WebP image information.
 *
 *     @type int|false    $width  Image width on success, false on failure.
 *     @type int|false    $height Image height on success, false on failure.
 *     @type string|false $type   The WebP type: one of 'lossy', 'lossless' or 'animated-alpha'.
 *                                False on failure.
 * }
 */
function wp_get_webp_info( $filename ) {
	$width  = false;
	$height = false;
	$type   = false;

	if ( 'image/webp' !== wp_get_image_mime( $filename ) ) {
		return compact( 'width', 'height', 'type' );
	}

	$magic = file_get_contents( $filename, false, null, 0, 40 );

	if ( false === $magic ) {
		return compact( 'width', 'height', 'type' );
	}

	// Make sure we got enough bytes.
	if ( strlen( $magic ) < 40 ) {
		return compact( 'width', 'height', 'type' );
	}

	/*
	 * The headers are a little different for each of the three formats.
	 * Header values based on WebP docs, see https://developers.google.com/speed/webp/docs/riff_container.
	 */
	switch ( substr( $magic, 12, 4 ) ) {
		// Lossy WebP.
		case 'VP8 ':
			$parts  = unpack( 'v2', substr( $magic, 26, 4 ) );
			$width  = (int) ( $parts[1] & 0x3FFF );
			$height = (int) ( $parts[2] & 0x3FFF );
			$type   = 'lossy';
			break;
		// Lossless WebP.
		case 'VP8L':
			$parts  = unpack( 'C4', substr( $magic, 21, 4 ) );
			$width  = (int) ( $parts[1] | ( ( $parts[2] & 0x3F ) << 8 ) ) + 1;
			$height = (int) ( ( ( $parts[2] & 0xC0 ) >> 6 ) | ( $parts[3] << 2 ) | ( ( $parts[4] & 0x03 ) << 10 ) ) + 1;
			$type   = 'lossless';
			break;
		// Animated/alpha WebP.
		case 'VP8X':
			// Pad 24-bit int.
			$width = unpack( 'V', substr( $magic, 24, 3 ) . "\x00" );
			$width = (int) ( $width[1] & 0xFFFFFF ) + 1;
			// Pad 24-bit int.
			$height = unpack( 'V', substr( $magic, 27, 3 ) . "\x00" );
			$height = (int) ( $height[1] & 0xFFFFFF ) + 1;
			$type   = 'animated-alpha';
			break;
	}

	return compact( 'width', 'height', 'type' );
}

/**
 * Gets loading optimization attributes.
 *
 * This function returns an array of attributes that should be merged into the given attributes array to optimize
 * loading performance. Potential attributes returned by this function are:
 * - `loading` attribute with a value of "lazy"
 * - `fetchpriority` attribute with a value of "high"
 * - `decoding` attribute with a value of "async"
 *
 * If any of these attributes are already present in the given attributes, they will not be modified. Note that no
 * element should have both `loading="lazy"` and `fetchpriority="high"`, so the function will trigger a warning in case
 * both attributes are present with those values.
 *
 * @since 6.3.0
 * @since 7.0.0 Support `fetchpriority=low` and `fetchpriority=auto` so that `loading=lazy` is not added and the media count is not increased.
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @param string $tag_name The tag name.
 * @param array  $attr     Array of the attributes for the tag.
 * @param string $context  Context for the element for which the loading optimization attribute is requested.
 * @return array Loading optimization attributes.
 */
function wp_get_loading_optimization_attributes( $tag_name, $attr, $context ) {
	global $wp_query;

	/**
	 * Filters whether to short-circuit loading optimization attributes.
	 *
	 * Returning an array from the filter will effectively short-circuit the loading of optimization attributes,
	 * returning that value instead.
	 *
	 * @since 6.4.0
	 *
	 * @param array|false $loading_attrs False by default, or array of loading optimization attributes to short-circuit.
	 * @param string      $tag_name      The tag name.
	 * @param array       $attr          Array of the attributes for the tag.
	 * @param string      $context       Context for the element for which the loading optimization attribute is requested.
	 */
	$loading_attrs = apply_filters( 'pre_wp_get_loading_optimization_attributes', false, $tag_name, $attr, $context );

	if ( is_array( $loading_attrs ) ) {
		return $loading_attrs;
	}

	$loading_attrs = array();

	/*
	 * Skip lazy-loading for the overall block template, as it is handled more granularly.
	 * The skip is also applicable for `fetchpriority`.
	 */
	if ( 'template' === $context ) {
		/** This filter is documented in wp-includes/media.php */
		return apply_filters( 'wp_get_loading_optimization_attributes', $loading_attrs, $tag_name, $attr, $context );
	}

	// For now this function only supports images and iframes.
	if ( 'img' !== $tag_name && 'iframe' !== $tag_name ) {
		/** This filter is documented in wp-includes/media.php */
		return apply_filters( 'wp_get_loading_optimization_attributes', $loading_attrs, $tag_name, $attr, $context );
	}

	/*
	 * Skip programmatically created images within content blobs as they need to be handled together with the other
	 * images within the post content or widget content.
	 * Without this clause, they would already be considered within their own context which skews the image count and
	 * can result in the first post content image being lazy-loaded or an image further down the page being marked as a
	 * high priority.
	 */
	if (
		'the_content' !== $context && doing_filter( 'the_content' ) ||
		'widget_text_content' !== $context && doing_filter( 'widget_text_content' ) ||
		'widget_block_content' !== $context && doing_filter( 'widget_block_content' )
	) {
		/** This filter is documented in wp-includes/media.php */
		return apply_filters( 'wp_get_loading_optimization_attributes', $loading_attrs, $tag_name, $attr, $context );

	}

	/*
	 * Add `decoding` with a value of "async" for every image unless it has a
	 * conflicting `decoding` attribute already present.
	 */
	if ( 'img' === $tag_name ) {
		$loading_attrs['decoding'] = $attr['decoding'] ?? 'async';
	}

	// For any resources, width and height must be provided, to avoid layout shifts.
	if ( ! isset( $attr['width'], $attr['height'] ) ) {
		/** This filter is documented in wp-includes/media.php */
		return apply_filters( 'wp_get_loading_optimization_attributes', $loading_attrs, $tag_name, $attr, $context );
	}

	/*
	 * The key function logic starts here.
	 */
	$maybe_in_viewport    = null;
	$increase_count       = false;
	$maybe_increase_count = false;

	// Logic to handle a `loading` attribute that is already provided.
	if ( isset( $attr['loading'] ) ) {
		/*
		 * Interpret "lazy" as not in viewport. Any other value can be
		 * interpreted as in viewport (realistically only "eager" or `false`
		 * to force-omit the attribute are other potential values).
		 */
		if ( 'lazy' === $attr['loading'] ) {
			$maybe_in_viewport = false;
		} else {
			$maybe_in_viewport = true;
		}
	}

	// Logic to handle a `fetchpriority` attribute that is already provided.
	$existing_fetchpriority = ( $attr['fetchpriority'] ?? null );
	$is_low_fetchpriority   = ( 'low' === $existing_fetchpriority );
	if ( 'high' === $existing_fetchpriority ) {
		/*
		 * If the image was already determined to not be in the viewport (e.g.
		 * from an already provided `loading` attribute), trigger a warning.
		 * Otherwise, the value can be interpreted as in viewport, since only
		 * the most important in-viewport image should have `fetchpriority` set
		 * to "high".
		 */
		if ( false === $maybe_in_viewport ) {
			_doing_it_wrong(
				__FUNCTION__,
				__( 'An image should not be lazy-loaded and marked as high priority at the same time.' ),
				'6.3.0'
			);
			/*
			 * Set `fetchpriority` here for backward-compatibility as we should
			 * not override what a developer decided, even though it seems
			 * incorrect.
			 */
			$loading_attrs['fetchpriority'] = 'high';
		} else {
			$maybe_in_viewport = true;
		}
	} elseif ( $is_low_fetchpriority ) {
		/*
		 * An IMG with fetchpriority=low is not initially displayed; it may be hidden in the Navigation Overlay,
		 * or it may be occluded in a non-initial carousel slide. Such images must not be lazy-loaded because the browser
		 * has no heuristic to know when to start loading them before the user needs to see them.
		 */
		$maybe_in_viewport = false;

		// Preserve fetchpriority=low.
		$loading_attrs['fetchpriority'] = 'low';
	} elseif ( 'auto' === $existing_fetchpriority ) {
		/*
		 * When a block's visibility support identifies that the block is conditionally displayed based on the viewport
		 * size, then it adds `fetchpriority=auto` to the block's IMG tags. These images must not be fetched with high
		 * priority because they could be erroneously loaded in viewports which do not even display them. Contrarily,
		 * they must not get `fetchpriority=low` because they may in fact be displayed in the current viewport. So as
		 * a signal to indicate that an IMG may be in the viewport, `fetchpriority=auto` is added. This has the effect
		 * here of preventing the media count from being increased, so that images hidden with block visibility do not
		 * affect whether a following IMG gets `loading=lazy`. In particular, `loading=lazy` should still be omitted
		 * on an IMG following any number of initial IMGs with `fetchpriority=auto` since those initial images may not
		 * be displayed.
		 */

		// Preserve fetchpriority=auto.
		$loading_attrs['fetchpriority'] = 'auto';
	}

	if ( null === $maybe_in_viewport ) {
		$header_enforced_contexts = array(
			'template_part_' . WP_TEMPLATE_PART_AREA_HEADER => true,
			'get_header_image_tag' => true,
		);

		/**
		 * Filters the header-specific contexts.
		 *
		 * @since 6.4.0
		 *
		 * @param array $default_header_enforced_contexts Map of contexts for which elements should be considered
		 *                                                in the header of the page, as $context => $enabled
		 *                                                pairs. The $enabled should always be true.
		 */
		$header_enforced_contexts = apply_filters( 'wp_loading_optimization_force_header_contexts', $header_enforced_contexts );

		// Consider elements with these header-specific contexts to be in viewport.
		if ( isset( $header_enforced_contexts[ $context ] ) ) {
			$maybe_in_viewport    = true;
			$maybe_increase_count = true;
		} elseif ( ! is_admin() && in_the_loop() && is_main_query() ) {
			/*
			 * Get the content media count, since this is a main query
			 * content element. This is accomplished by "increasing"
			 * the count by zero, as the only way to get the count is
			 * to call this function.
			 * The actual count increase happens further below, based
			 * on the `$increase_count` flag set here.
			 */
			$content_media_count = wp_increase_content_media_count( 0 );
			$increase_count      = true;

			// If the count so far is below the threshold, `loading` attribute is omitted.
			if ( $content_media_count < wp_omit_loading_attr_threshold() ) {
				$maybe_in_viewport = true;
			} else {
				$maybe_in_viewport = false;
			}
		} elseif (
			// Only apply for main query but before the loop.
			$wp_query->before_loop && $wp_query->is_main_query()
			/*
			 * Any image before the loop, but after the header has started should not be lazy-loaded,
			 * except when the footer has already started which can happen when the current template
			 * does not include any loop.
			 */
			&& did_action( 'get_header' ) && ! did_action( 'get_footer' )
		) {
			$maybe_in_viewport    = true;
			$maybe_increase_count = true;
		}
	}

	/*
	 * If the element is in the viewport (`true`), potentially add
	 * `fetchpriority` with a value of "high". Otherwise, i.e. if the element
	 * is not in the viewport (`false`) or it is unknown (`null`), add
	 * `loading` with a value of "lazy" if the element is not already being
	 * de-prioritized with `fetchpriority=low` due to occlusion in
	 * Navigation Overlay, non-initial carousel slides, or a collapsed Details block.
	 */
	if ( $maybe_in_viewport ) {
		$loading_attrs = wp_maybe_add_fetchpriority_high_attr( $loading_attrs, $tag_name, $attr );
	} elseif ( ! $is_low_fetchpriority ) {
		// Only add `loading="lazy"` if the feature is enabled.
		if ( wp_lazy_loading_enabled( $tag_name, $context ) ) {
			$loading_attrs['loading'] = 'lazy';
		}
	}

	/*
	 * If flag was set based on contextual logic above, increase the content
	 * media count, either unconditionally, or based on whether the image size
	 * is larger than the threshold. This does not apply when the IMG has
	 * fetchpriority=auto because it may be conditionally displayed by viewport
	 * size.
	 */
	if ( 'auto' !== $existing_fetchpriority ) {
		if ( $increase_count ) {
			wp_increase_content_media_count();
		} elseif ( $maybe_increase_count ) {
			/** This filter is documented in wp-includes/media.php */
			$wp_min_priority_img_pixels = apply_filters( 'wp_min_priority_img_pixels', 50000 );

			if ( $wp_min_priority_img_pixels <= $attr['width'] * $attr['height'] ) {
				wp_increase_content_media_count();
			}
		}
	}

	/**
	 * Filters the loading optimization attributes.
	 *
	 * @since 6.4.0
	 *
	 * @param array  $loading_attrs The loading optimization attributes.
	 * @param string $tag_name      The tag name.
	 * @param array  $attr          Array of the attributes for the tag.
	 * @param string $context       Context for the element for which the loading optimization attribute is requested.
	 */
	return apply_filters( 'wp_get_loading_optimization_attributes', $loading_attrs, $tag_name, $attr, $context );
}

/**
 * Gets the threshold for how many of the first content media elements to not lazy-load.
 *
 * This function runs the {@see 'wp_omit_loading_attr_threshold'} filter, which uses a default threshold value of 3.
 * The filter is only run once per page load, unless the `$force` parameter is used.
 *
 * @since 5.9.0
 *
 * @param bool $force Optional. If set to true, the filter will be (re-)applied even if it already has been before.
 *                    Default false.
 * @return int The number of content media elements to not lazy-load.
 */
function wp_omit_loading_attr_threshold( $force = false ) {
	static $omit_threshold;

	// This function may be called multiple times. Run the filter only once per page load.
	if ( ! isset( $omit_threshold ) || $force ) {
		/**
		 * Filters the threshold for how many of the first content media elements to not lazy-load.
		 *
		 * For these first content media elements, the `loading` attribute will be omitted. By default, this is the case
		 * for only the very first content media element.
		 *
		 * @since 5.9.0
		 * @since 6.3.0 The default threshold was changed from 1 to 3.
		 *
		 * @param int $omit_threshold The number of media elements where the `loading` attribute will not be added. Default 3.
		 */
		$omit_threshold = apply_filters( 'wp_omit_loading_attr_threshold', 3 );
	}

	return $omit_threshold;
}

/**
 * Increases an internal content media count variable.
 *
 * @since 5.9.0
 * @access private
 *
 * @param int $amount Optional. Amount to increase by. Default 1.
 * @return int The latest content media count, after the increase.
 */
function wp_increase_content_media_count( $amount = 1 ) {
	static $content_media_count = 0;

	$content_media_count += $amount;

	return $content_media_count;
}

/**
 * Determines whether to add `fetchpriority='high'` to loading attributes.
 *
 * @since 6.3.0
 * @since 7.0.0 Support is added for IMG tags with `fetchpriority='low'` and `fetchpriority='auto'`.
 * @access private
 *
 * @param array<string, string> $loading_attrs Array of the loading optimization attributes for the element.
 * @param string                $tag_name      The tag name.
 * @param array<string, mixed>  $attr          Array of the attributes for the element.
 * @return array<string, string> Updated loading optimization attributes for the element.
 */
function wp_maybe_add_fetchpriority_high_attr( $loading_attrs, $tag_name, $attr ) {
	// For now, adding `fetchpriority="high"` is only supported for images.
	if ( 'img' !== $tag_name ) {
		return $loading_attrs;
	}

	$existing_fetchpriority = $attr['fetchpriority'] ?? null;
	if ( null !== $existing_fetchpriority && 'auto' !== $existing_fetchpriority ) {
		/*
		 * When an IMG has been explicitly marked with `fetchpriority=high`, then honor that this is the element that
		 * should have the priority. In contrast, the Navigation block may add `fetchpriority=low` to an IMG which
		 * appears in the Navigation Overlay; such images should never be considered candidates for
		 * `fetchpriority=high`. Lastly, block visibility may add `fetchpriority=auto` to an IMG when the block is
		 * conditionally displayed based on viewport size. Such an image is considered an LCP element candidate if it
		 * exceeds the threshold for the minimum number of square pixels.
		 */
		if ( 'high' === $existing_fetchpriority ) {
			$loading_attrs['fetchpriority'] = 'high';
			wp_high_priority_element_flag( false );
		}

		return $loading_attrs;
	}

	// Lazy-loading and `fetchpriority="high"` are mutually exclusive.
	if ( isset( $loading_attrs['loading'] ) && 'lazy' === $loading_attrs['loading'] ) {
		return $loading_attrs;
	}

	if ( ! wp_high_priority_element_flag() ) {
		return $loading_attrs;
	}

	/**
	 * Filters the minimum square-pixels threshold for an image to be eligible as the high-priority image.
	 *
	 * @since 6.3.0
	 *
	 * @param int $threshold Minimum square-pixels threshold. Default 50000.
	 */
	$wp_min_priority_img_pixels = apply_filters( 'wp_min_priority_img_pixels', 50000 );

	if ( $wp_min_priority_img_pixels <= $attr['width'] * $attr['height'] ) {
		if ( 'auto' !== $existing_fetchpriority ) {
			$loading_attrs['fetchpriority'] = 'high';
		}
		wp_high_priority_element_flag( false );
	}

	return $loading_attrs;
}

/**
 * Accesses a flag that indicates if an element is a possible candidate for `fetchpriority='high'`.
 *
 * @since 6.3.0
 * @access private
 *
 * @param bool $value Optional. Used to change the static variable. Default null.
 * @return bool Returns true if the high-priority element was not already marked.
 */
function wp_high_priority_element_flag( $value = null ): bool {
	static $high_priority_element = true;

	if ( is_bool( $value ) ) {
		$high_priority_element = $value;
	}

	return $high_priority_element;
}

/**
 * Determines the output format for the image editor.
 *
 * @since 6.7.0
 * @access private
 *
 * @param string $filename  Path to the image.
 * @param string $mime_type The source image mime type.
 * @return array<string, string> An array of mime type mappings.
 */
function wp_get_image_editor_output_format( $filename, $mime_type ) {
	$output_format = array(
		'image/heic'          => 'image/jpeg',
		'image/heif'          => 'image/jpeg',
		'image/heic-sequence' => 'image/jpeg',
		'image/heif-sequence' => 'image/jpeg',
	);

	/**
	 * Filters the image editor output format mapping.
	 *
	 * Enables filtering the mime type used to save images. By default HEIC/HEIF images
	 * are converted to JPEGs.
	 *
	 * @see WP_Image_Editor::get_output_format()
	 *
	 * @since 5.8.0
	 * @since 6.7.0 The default was changed from an empty array to an array
	 *              containing the HEIC/HEIF images mime types.
	 *
	 * @param array<string, string> $output_format An array of mime type mappings. Maps a source mime type to a new
	 *                                             destination mime type. By default maps HEIC/HEIF input to JPEG output.
	 * @param string                $filename      Path to the image.
	 * @param string                $mime_type     The source image mime type.
	 */
	return apply_filters( 'image_editor_output_format', $output_format, $filename, $mime_type );
}

/**
 * Checks whether client-side media processing is enabled.
 *
 * Client-side media processing uses the browser's capabilities to handle
 * tasks like image resizing and compression before uploading to the server.
 *
 * @since 7.1.0
 *
 * @return bool Whether client-side media processing is enabled.
 */
function wp_is_client_side_media_processing_enabled(): bool {
	// This is due to SharedArrayBuffer requiring a secure context.
	$host    = strtolower( (string) strtok( $_SERVER['HTTP_HOST'] ?? '', ':' ) );
	$enabled = ( is_ssl() || 'localhost' === $host || str_ends_with( $host, '.localhost' ) );

	/**
	 * Filters whether client-side media processing is enabled.
	 *
	 * @since 7.1.0
	 *
	 * @param bool $enabled Whether client-side media processing is enabled. Default true if the page is served in a secure context.
	 */
	return (bool) apply_filters( 'wp_client_side_media_processing_enabled', $enabled );
}

/**
 * Sets a global JS variable to indicate that client-side media processing is enabled.
 *
 * @since 7.1.0
 */
function wp_set_client_side_media_processing_flag(): void {
	if ( ! wp_is_client_side_media_processing_enabled() ) {
		return;
	}

	wp_add_inline_script( 'wp-block-editor', 'window.__clientSideMediaProcessing = true;', 'before' );

	$chromium_version = wp_get_chromium_major_version();

	if ( null !== $chromium_version && $chromium_version >= 137 ) {
		wp_add_inline_script( 'wp-block-editor', 'window.__documentIsolationPolicy = true;', 'before' );
	}
}

/**
 * Returns the major Chrome/Chromium version from the current request's User-Agent.
 *
 * Matches all Chromium-based browsers (Chrome, Edge, Opera, Brave).
 *
 * @since 7.1.0
 *
 * @return int|null The major Chrome version, or null if not a Chromium browser.
 */
function wp_get_chromium_major_version(): ?int {
	if ( empty( $_SERVER['HTTP_USER_AGENT'] ) ) {
		return null;
	}
	if ( preg_match( '#Chrome/(\d+)#', $_SERVER['HTTP_USER_AGENT'], $matches ) ) {
		return (int) $matches[1];
	}
	return null;
}

/**
 * Enables cross-origin isolation in the block editor.
 *
 * Required for enabling SharedArrayBuffer for WebAssembly-based
 * media processing in the editor. Uses Document-Isolation-Policy
 * on supported browsers (Chromium 137+).
 *
 * Skips setup when a third-party page builder overrides the block
 * editor via a custom `action` query parameter, as DIP would block
 * same-origin iframe access that these editors rely on.
 *
 * @since 7.1.0
 */
function wp_set_up_cross_origin_isolation(): void {
	if ( ! wp_is_client_side_media_processing_enabled() ) {
		return;
	}

	$screen = get_current_screen();

	if ( ! $screen ) {
		return;
	}

	if ( ! $screen->is_block_editor() && 'site-editor' !== $screen->id && ! ( 'widgets' === $screen->id && wp_use_widgets_block_editor() ) ) {
		return;
	}

	/*
	 * Skip when rendering the classic-theme home route, which shows the site
	 * preview in an iframe and must reach its `contentDocument` to neutralize
	 * interactive 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();
}