wp_finalize_template_enhancement_output_buffer( string $output, int $phase ): string

924function wp_finalize_template_enhancement_output_buffer( string $output, int $phase ): string {925	// When the output is being cleaned (e.g. pending template is replaced with error page), do not send it through the filter.926	if ( ( $phase & PHP_OUTPUT_HANDLER_CLEAN ) !== 0 ) {927		return $output;928	}929 930	// Detect if the response is an HTML content type.931	$is_html_content_type = null;932	$html_content_types   = array( 'text/html', 'application/xhtml+xml' );933	foreach ( headers_list() as $header ) {934		$header_parts = explode( ':', strtolower( $header ), 2 );935		if (936			count( $header_parts ) === 2 &&937			'content-type' === $header_parts[0]938		) {939			/*940			 * This is looking for very specific content types, therefore it941			 * doesn’t need to fully parse the header’s value. Instead, it needs942			 * only assert that the content type is one of the static HTML types.943			 *944			 * Example:945			 *946			 *     Content-Type: text/html; charset=utf8947			 *     Content-Type: text/html  ;charset=latin4948			 *     Content-Type:application/xhtml+xml949			 */950			$media_type           = trim( strtok( $header_parts[1], ';' ), " \t" );951			$is_html_content_type = in_array( $media_type, $html_content_types, true );952			break; // PHP only sends the first Content-Type header in the list.953		}954	}955	if ( null === $is_html_content_type ) {956		$is_html_content_type = in_array( ini_get( 'default_mimetype' ), $html_content_types, true );957	}958 959	// If the content type is not HTML, short-circuit since it is not relevant for enhancement.960	if ( ! $is_html_content_type ) {961		/** This action is documented in wp-includes/template.php */962		do_action( 'wp_finalized_template_enhancement_output_buffer', $output );963		return $output;964	}965 966	$filtered_output = $output;967 968	$did_just_catch = false;969 970	$error_log = array();971	set_error_handler(972		static function ( int $level, string $message, ?string $file = null, ?int $line = null ) use ( &$error_log, &$did_just_catch ) {973			// Switch a user error to an exception so that it can be caught and the buffer can be returned.974			if ( E_USER_ERROR === $level ) {975				throw new Exception( __( 'User error triggered:' ) . ' ' . $message );976			}977 978			// Display a caught exception as an error since it prevents any of the output buffer filters from applying.979			if ( $did_just_catch ) {980				$level = E_USER_ERROR;981			}982 983			// Capture a reported error to be displayed by appending to the processed output buffer if display_errors is enabled.984			if ( error_reporting() & $level ) {985				$error_log[] = compact( 'level', 'message', 'file', 'line' );986			}987			return false;988		}989	);990	$original_display_errors = ini_get( 'display_errors' );991	if ( $original_display_errors ) {992		ini_set( 'display_errors', 0 );993	}994 995	try {996		/**997		 * Filters the template enhancement output buffer prior to sending to the client.998		 *999		 * This filter only applies the HTML output of an included template. This filter is a progressive enhancement1000		 * intended for applications such as optimizing markup to improve frontend page load performance. Sites must not1001		 * depend on this filter applying since they may opt to stream the responses instead. Callbacks for this filter1002		 * are highly discouraged from using regular expressions to do any kind of replacement on the output. Use the1003		 * HTML API (either `WP_HTML_Tag_Processor` or `WP_HTML_Processor`), or else use {@see DOM\HtmlDocument} as of
When	Instructions	Calls it makes
`$level !== 256 && !$level`	14–15	`error_reporting()`
`$level === 256`	17	`__()`
`$level !== 256 && $level`	22–23	`error_reporting(), compact()`
PHP	Compiled	Executed	Branches	Notes
8.6-dev	212	14–23	19
8.5	212	14–23	19
8.4	212	14–23	19	9 fewer instructions than PHP 8.3
8.3	221	14–23	19
8.2	221	14–23	19	1 more instruction than PHP 8.1
8.1	220	14–23	19
7.4	220	14–23	19