code: public function toggle(string $token):bool {
  		if($this->contains($token)) {
  			$this->remove($token);
  
  			return false;
  		}
  
  		$this->add($token);
  
  		return true;
  	}
docs: Removes $token from the underlying attribute value and returns false. If
  $token doesn't exist, it's added and the function returns true.
  @param string $token
  @return bool true if token is added, false if token is removed.