core-bundle/src/Resources/contao/library/Contao/Validator.php
public static function isUrl($varValue)
	{
		try
		{
			$varValue = Idna::encodeUrl($varValue);
		}
		catch (\InvalidArgumentException $e) {}

		return preg_match('/^[\w\/.*+?$#%:,;{}()[\]@&!=~|-]+$/u', $varValue);
	}
public static function isUrl($varValue)
	{
		try
		{
			$varValue = Idna::encodeUrl($varValue);
		}
		catch (\InvalidArgumentException $e) {}

		return preg_match('/^[\w\/.*+?$#%:,;{}()[\]@&!=~|-]+$/u', $varValue);
	}
Valid URL with special characters allowed (see #6402)

@param mixed $varValue The value to be validated

@return boolean True if the value is a valid URL