wp-includes/class-wp-xmlrpc-server.php:379Sends error response to client.
$errorIXR_Error|string$messagefalseoptionalfalse public function error( $error, $message = false ) { // Accepts either an error object or an error code and message if ( $message && ! is_object( $error ) ) { $error = new IXR_Error( $error, $message ); } if ( ! $this->is_enabled ) { status_header( $error->code ); } $this->output( $error->getXml() ); }Introduced in 5.7.3. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-xmlrpc-server.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.