core-bundle/src/Resources/contao/library/Contao/Config.php
public function add($strKey, $varValue)
	{
		$this->markModified();
		$this->arrData[$strKey] = $this->escape($varValue) . ';';
	}
public function add($strKey, $varValue)
	{
		$this->markModified();
		$this->arrData[$strKey] = $this->escape($varValue) . ';';
	}
Add a configuration variable to the local configuration file

@param string $strKey   The full variable name
@param mixed  $varValue The configuration value