code: public static function persist($strKey, $varValue)
  	{
  		$objConfig = static::getInstance();
  
  		if (strncmp($strKey, '$GLOBALS', 8) !== 0)
  		{
  			$strKey = "\$GLOBALS['TL_CONFIG']['$strKey']";
  		}
  
  		$objConfig->add($strKey, $varValue);
  	}
docs: Permanently set a configuration value
  
  @param string $strKey   The short key or full variable name
  @param mixed  $varValue The configuration value