diff --git a/src/wp-includes/class-wp-error.php b/src/wp-includes/class-wp-error.php
index 225460b472..e22357ac28 100644
--- a/src/wp-includes/class-wp-error.php
+++ b/src/wp-includes/class-wp-error.php
@@ -56,11 +56,7 @@ class WP_Error {
 			return;
 		}
 
-		$this->errors[ $code ][] = $message;
-
-		if ( ! empty( $data ) ) {
-			$this->error_data[ $code ] = $data;
-		}
+		$this->add( $code, $message, $data );
 	}
 
 	/**
@@ -176,7 +172,7 @@ class WP_Error {
 	}
 
 	/**
-	 * Add an error or append additional message to an existing error.
+	 * Adds an error or appends an additional message to an existing error.
 	 *
 	 * @since 2.1.0
 	 *
@@ -186,9 +182,22 @@ class WP_Error {
 	 */
 	public function add( $code, $message, $data = '' ) {
 		$this->errors[ $code ][] = $message;
+
 		if ( ! empty( $data ) ) {
-			$this->error_data[ $code ] = $data;
+			$this->add_data( $data, $code );
 		}
+
+		/**
+		 * Fires when an error is added to a WP_Error object.
+		 *
+		 * @since 5.6.0
+		 *
+		 * @param string|int $code     Error code.
+		 * @param string     $message  Error message.
+		 * @param mixed      $data     Error data. Might be empty.
+		 * @param WP_Error   $wp_error The WP_Error object.
+		 */
+		do_action( 'wp_error_added', $code, $message, $data, $this );
 	}
 
 	/**
diff --git a/src/wp-includes/load.php b/src/wp-includes/load.php
index 0cec068fd7..7a79fc1a63 100644
--- a/src/wp-includes/load.php
+++ b/src/wp-includes/load.php
@@ -1446,17 +1446,30 @@ function wp_doing_cron() {
 }
 
 /**
- * Check whether variable is a WordPress Error.
+ * Checks whether the given variable is a WordPress Error.
  *
- * Returns true if $thing is an object of the WP_Error class.
+ * Returns whether `$thing` is an instance of the `WP_Error` class.
  *
  * @since 2.1.0
  *
- * @param mixed $thing Check if unknown variable is a WP_Error object.
- * @return bool True, if WP_Error. False, if not WP_Error.
+ * @param mixed $thing The variable to check.
+ * @return bool Whether the variable is an instance of WP_Error.
  */
 function is_wp_error( $thing ) {
-	return ( $thing instanceof WP_Error );
+	$is = ( $thing instanceof WP_Error );
+
+	if ( $is ) {
+		/**
+		 * Fires when `is_wp_error()` is called and it's an instance of `WP_Error`.
+		 *
+		 * @since 5.6.0
+		 *
+		 * @param WP_Error $thing The error object passed to `is_wp_error()`.
+		 */
+		do_action( 'wp_error_checked', $thing );
+	}
+
+	return $is;
 }
 
 /**