public function setPrefix($prefix = null) {

		if(null !== $prefix) {

			if(false === is_string($prefix)) {
				return trigger_error(sprintf('Argument 1 passed to %s() must be of the type string, "%s" given', __METHOD__, gettype($prefix)), E_USER_ERROR);
			}

			$this -> prefix = $prefix;
		}

		return $this;
	}