system/Session/Session.php
public function setTempdata($data, $value = null, int $ttl = 300)
	{
		$this->set($data, $value);
		$this->markAsTempdata($data, $ttl);
	}
public function setTempdata($data, $value = null, int $ttl = 300)
	{
		$this->set($data, $value);
		$this->markAsTempdata($data, $ttl);
	}
Sets new data into the session, and marks it as temporary data
with a set lifespan.

@param string|array $data  Session data key or associative array of items
@param null         $value Value to store
@param integer      $ttl   Time-to-live in seconds