WP_REST_Users_Controller::check_username( string $value, WP_REST_Request $request, string $param ): string|WP_Error

1318	public function check_username( $value, $request, $param ) {1319		$username = (string) $value;1320 1321		if ( ! validate_username( $username ) ) {1322			return new WP_Error(1323				'rest_user_invalid_username',1324				__( 'This username is invalid because it uses illegal characters. Please enter a valid username.' ),1325				array( 'status' => 400 )1326			);1327		}1328 1329		/** This filter is documented in wp-includes/user.php */1330		$illegal_logins = (array) apply_filters( 'illegal_user_logins', array() );1331 1332		if ( in_array( strtolower( $username ), array_map( 'strtolower', $illegal_logins ), true ) ) {1333			return new WP_Error(1334				'rest_user_invalid_username',1335				__( 'Sorry, that username is not allowed.' ),1336				array( 'status' => 400 )1337			);1338		}1339 1340		return $username;1341	}