core-bundle/src/Resources/contao/library/Contao/Input.php
public static function encodeSpecialChars($varValue)
	{
		if ($varValue === null || $varValue == '')
		{
			return $varValue;
		}

		// Recursively clean arrays
		if (\is_array($varValue))
		{
			foreach ($varValue as $k=>$v)
			{
				$varValue[$k] = static::encodeSpecialChars($v);
			}

			return $varValue;
		}

		$arrSearch = array('#', '<', '>', '(', ')', '\\', '=');
		$arrReplace = array('&#35;', '&#60;', '&#62;', '&#40;', '&#41;', '&#92;', '&#61;');

		return str_replace($arrSearch, $arrReplace, $varValue);
	}
public static function encodeSpecialChars($varValue)
	{
		if ($varValue === null || $varValue == '')
		{
			return $varValue;
		}

		// Recursively clean arrays
		if (\is_array($varValue))
		{
			foreach ($varValue as $k=>$v)
			{
				$varValue[$k] = static::encodeSpecialChars($v);
			}

			return $varValue;
		}

		$arrSearch = array('#', '<', '>', '(', ')', '\\', '=');
		$arrReplace = array('&#35;', '&#60;', '&#62;', '&#40;', '&#41;', '&#92;', '&#61;');

		return str_replace($arrSearch, $arrReplace, $varValue);
	}
Encode special characters which are potentially dangerous

@param mixed $varValue A string or array

@return mixed The encoded string or array