--- a/wp/wp-includes/class-wp-fatal-error-handler.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/class-wp-fatal-error-handler.php	Tue Dec 15 13:49:49 2020 +0100
@@ -3,7 +3,7 @@
  * Error Protection API: WP_Fatal_Error_Handler class
  *
  * @package WordPress
- * @since   5.2.0
+ * @since 5.2.0
  */
 
 /**
@@ -30,6 +30,11 @@
 			return;
 		}
 
+		// Do not trigger the fatal error handler while updates are being installed.
+		if ( wp_is_maintenance_mode() ) {
+			return;
+		}
+
 		try {
 			// Bail if no error found.
 			$error = $this->detect_error();
@@ -41,13 +46,15 @@
 				load_default_textdomain();
 			}
 
+			$handled = false;
+
 			if ( ! is_multisite() && wp_recovery_mode()->is_initialized() ) {
-				wp_recovery_mode()->handle_error( $error );
+				$handled = wp_recovery_mode()->handle_error( $error );
 			}
 
 			// Display the PHP error template if headers not sent.
 			if ( is_admin() || ! headers_sent() ) {
-				$this->display_error_template( $error );
+				$this->display_error_template( $error, $handled );
 			}
 		} catch ( Exception $e ) {
 			// Catch exceptions and remain silent.
@@ -125,10 +132,12 @@
 	 * If no such drop-in is available, this will call {@see WP_Fatal_Error_Handler::display_default_error_template()}.
 	 *
 	 * @since 5.2.0
+	 * @since 5.3.0 The `$handled` parameter was added.
 	 *
-	 * @param array $error Error information retrieved from `error_get_last()`.
+	 * @param array         $error   Error information retrieved from `error_get_last()`.
+	 * @param true|WP_Error $handled Whether Recovery Mode handled the fatal error.
 	 */
-	protected function display_error_template( $error ) {
+	protected function display_error_template( $error, $handled ) {
 		if ( defined( 'WP_CONTENT_DIR' ) ) {
 			// Load custom PHP error template, if present.
 			$php_error_pluggable = WP_CONTENT_DIR . '/php-error.php';
@@ -140,7 +149,7 @@
 		}
 
 		// Otherwise, display the default error template.
-		$this->display_default_error_template( $error );
+		$this->display_default_error_template( $error, $handled );
 	}
 
 	/**
@@ -153,10 +162,12 @@
 	 * be used to modify these parameters.
 	 *
 	 * @since 5.2.0
+	 * @since 5.3.0 The `$handled` parameter was added.
 	 *
-	 * @param array $error Error information retrieved from `error_get_last()`.
+	 * @param array         $error   Error information retrieved from `error_get_last()`.
+	 * @param true|WP_Error $handled Whether Recovery Mode handled the fatal error.
 	 */
-	protected function display_default_error_template( $error ) {
+	protected function display_default_error_template( $error, $handled ) {
 		if ( ! function_exists( '__' ) ) {
 			wp_load_translations_early();
 		}
@@ -169,12 +180,22 @@
 			require_once ABSPATH . WPINC . '/class-wp-error.php';
 		}
 
-		if ( is_protected_endpoint() ) {
-			$message = __( 'The site is experiencing technical difficulties. Please check your site admin email inbox for instructions.' );
+		if ( true === $handled && wp_is_recovery_mode() ) {
+			$message = __( 'There has been a critical error on your website, putting it in recovery mode. Please check the Themes and Plugins screens for more details. If you just installed or updated a theme or plugin, check the relevant page for that first.' );
+		} elseif ( is_protected_endpoint() ) {
+			$message = __( 'There has been a critical error on your website. Please check your site admin email inbox for instructions.' );
 		} else {
-			$message = __( 'The site is experiencing technical difficulties.' );
+			$message = __( 'There has been a critical error on your website.' );
 		}
 
+		$message = sprintf(
+			'<p>%s</p><p><a href="%s">%s</a></p>',
+			$message,
+			/* translators: Documentation explaining debugging in WordPress. */
+			__( 'https://wordpress.org/support/article/debugging-in-wordpress/' ),
+			__( 'Learn more about debugging in WordPress.' )
+		);
+
 		$args = array(
 			'response' => 500,
 			'exit'     => false,